Go with souble quotes. (See https://github.com/skywinder/github-changelog-generator/pull/220#discussion_r27262657 )

spec/spec_helper.rb

@@ -15,9 +15,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-require 'codeclimate-test-reporter'
-require 'simplecov'
-require 'coveralls'
+require "codeclimate-test-reporter"
+require "simplecov"
+require "coveralls"
 
 SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
   Coveralls::SimpleCov::Formatter,
@@ -26,7 +26,7 @@ SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
 ]
 SimpleCov.start
 
-require 'github_changelog_generator'
+require "github_changelog_generator"
 
 # This file was generated by the `rspec --init` command. Conventionally, all
 # specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
@@ -95,7 +95,7 @@ RSpec.configure do |config|
     # Use the documentation formatter for detailed output,
     # unless a formatter has already been configured
     # (e.g. via a command-line flag).
-    config.default_formatter = 'doc'
+    config.default_formatter = "doc"
   end
 
   # Print the 10 slowest examples and example groups at the