update gemfile

Author: chamnap

Gemfile

@@ -4,7 +4,8 @@ gem "bundler",          "~> 1.5.3"
 gem "rake",             "~> 10.2.2"
 gem "rspec",            "~> 2.14.1"
 gem "pry",              "~> 0.9.12.6"
-gem "coveralls",        require: false
+gem "simplecov",        "~> 0.8.2"
+gem "coveralls",        "~> 0.7.0", require: false
 gem "codeclimate-test-reporter"
 gem "ammeter",          "~> 1.0.0"
 gem "railties"