Change coverage output format to json

Author: Umekawa

spec/spec_helper.rb

@@ -1,6 +1,14 @@
 if ENV["CI"]
   require "simplecov"
-  SimpleCov.start
+  require "simplecov_json_formatter"
+  SimpleCov.start do
+    SimpleCov.formatters = [
+      SimpleCov::Formatter::JSONFormatter,
+      SimpleCov::Formatter::HTMLFormatter
+    ]
+
+    add_filter "/spec/"
+  end
 end
 
 require "qiita-markdown"