Fix README example

Author: sfackler

README.md

@@ -18,10 +18,9 @@ use std::thread;
 use r2d2_postgres::{TlsMode, PostgresConnectionManager};
 
 fn main() {
-    let config = r2d2::Config::default();
     let manager = PostgresConnectionManager::new("postgres://postgres@localhost",
                                                  TlsMode::None).unwrap();
-    let pool = r2d2::Pool::new(config, manager).unwrap();
+    let pool = r2d2::Pool::new(manager).unwrap();
 
     for i in 0..10i32 {
         let pool = pool.clone();