Update pip to 18.1

[pyup-bot]

This PR updates pip from 10.0.1 to 18.1.

Changelog

18.1

=================

Features
--------

- Allow PEP 508 URL requirements to be used as dependencies.

As a security measure, pip will raise an exception when installing packages from
PyPI if those packages depend on packages not also hosted on PyPI.
In the future, PyPI will block uploading packages with such external URL dependencies directly. (`4187 <https://github.com/pypa/pip/issues/4187>`_)
- Upgrade pyparsing to 2.2.1. (`5013 <https://github.com/pypa/pip/issues/5013>`_)
- Allows dist options (--abi, --python-version, --platform, --implementation) when installing with --target (`5355 <https://github.com/pypa/pip/issues/5355>`_)
- Support passing ``svn+ssh`` URLs with a username to ``pip install -e``. (`5375 <https://github.com/pypa/pip/issues/5375>`_)
- pip now ensures that the RECORD file is sorted when installing from a wheel file. (`5525 <https://github.com/pypa/pip/issues/5525>`_)
- Add support for Python 3.7. (`5561 <https://github.com/pypa/pip/issues/5561>`_)
- Malformed configuration files now show helpful error messages, instead of tracebacks. (`5798 <https://github.com/pypa/pip/issues/5798>`_)

Bug Fixes
---------

- Checkout the correct branch when doing an editable Git install. (`2037 <https://github.com/pypa/pip/issues/2037>`_)
- Run self-version-check only on commands that may access the index, instead of
trying on every run and failing to do so due to missing options. (`5433 <https://github.com/pypa/pip/issues/5433>`_)
- Allow a Git ref to be installed over an existing installation. (`5624 <https://github.com/pypa/pip/issues/5624>`_)
- Show a better error message when a configuration option has an invalid value. (`5644 <https://github.com/pypa/pip/issues/5644>`_)
- Always revalidate cached simple API pages instead of blindly caching them for up to 10
minutes. (`5670 <https://github.com/pypa/pip/issues/5670>`_)
- Avoid caching self-version-check information when cache is disabled. (`5679 <https://github.com/pypa/pip/issues/5679>`_)
- Avoid traceback printing on autocomplete after flags in the CLI. (`5751 <https://github.com/pypa/pip/issues/5751>`_)
- Fix incorrect parsing of egg names if pip needs to guess the package name. (`5819 <https://github.com/pypa/pip/issues/5819>`_)

Vendored Libraries
------------------

- Upgrade certifi to 2018.8.24
- Upgrade packaging to 18.0
- Add pep517 version 0.2
- Upgrade pytoml to 0.1.19
- Upgrade pkg_resources to 40.4.3 (via setuptools)

Improved Documentation
----------------------

- Fix "Requirements Files" reference in User Guide (`user_guide_fix_requirements_file_ref <https://github.com/pypa/pip/issues/user_guide_fix_requirements_file_ref>`_)

18.0

=================

Process
-------

- Switch to a Calendar based versioning scheme.
- Formally document our deprecation process as a minimum of 6 months of deprecation
warnings.
- Adopt and document NEWS fragment writing style.
- Switch to releasing a new, non bug fix version of pip every 3 months.

Deprecations and Removals
-------------------------

- Remove the legacy format from pip list. (3651, 3654)
- Dropped support for Python 3.3. (3796)
- Remove support for cleaning up egg fragment postfixes. (4174)
- Remove the shim for the old get-pip.py location. (5520)

For the past 2 years, it's only been redirecting users to use the newer
https://bootstrap.pypa.io/get-pip.py location.

Features
--------

- Introduce a new --prefer-binary flag, to prefer older wheels over newer source packages. (3785)
- Improve autocompletion function on file name completion after options
which have ``<file>``, ``<dir>`` or ``<path>`` as metavar. (4842, 5125)
- Add support for installing PEP 518 build dependencies from source. (5229)
- Improve status message when upgrade is skipped due to only-if-needed strategy. (5319)

Bug Fixes
---------

- Update pip's self-check logic to not use a virtualenv specific file and honor cache-dir. (3905)
- Remove compiled pyo files for wheel packages. (4471)
- Speed up printing of newly installed package versions. (5127)
- Restrict install time dependency warnings to directly-dependant packages. (5196, 5457)

Warning about the entire package set has resulted in users getting confused as
to why pip is printing these warnings.
- Improve handling of PEP 518 build requirements: support environment markers and extras. (5230, 5265)
- Remove username/password from log message when using index with basic auth. (5249)
- Remove trailing os.sep from PATH directories to avoid false negatives. (5293)
- Fix "pip wheel pip" being blocked by the "don't use pip to modify itself" check. (5311, 5312)
- Disable pip's version check (and upgrade message) when installed by a different package manager. (5346)

This works better with Linux distributions where pip's upgrade message may
result in users running pip in a manner that modifies files that should be
managed by the OS's package manager.
- Check for file existence and unlink first when clobbering existing files during a wheel install. (5366)
- Improve error message to be more specific when no files are found as listed in as listed in PKG-INFO. (5381)
- Always read ``pyproject.toml`` as UTF-8. This fixes Unicode handling on Windows and Python 2. (5482)
- Fix a crash that occurs when PATH not set, while generating script location warning. (5558)
- Disallow packages with ``pyproject.toml`` files that have an empty build-system table. (5627)

Vendored Libraries
------------------

- Update CacheControl to 0.12.5.
- Update certifi to 2018.4.16.
- Update distro to 1.3.0.
- Update idna to 2.7.
- Update ipaddress to 1.0.22.
- Update pkg_resources to 39.2.0 (via setuptools).
- Update progress to 1.4.
- Update pytoml to 0.1.16.
- Update requests to 2.19.1.
- Update urllib3 to 1.23.

Improved Documentation
----------------------

- Document how to use pip with a proxy server. (512, 5574)
- Document that the output of pip show is in RFC-compliant mail header format. (5261)

Links

• PyPI: https://pypi.org/project/pip
• Changelog: https://pyup.io/changelogs/pip/
• Homepage: https://pip.pypa.io/

[pyup-bot]

Closing this in favor of #81