Pinned Rubocop to 0.57.2

Rubocop 0.58 has dropped support for ruby 2.1 and now throws.
Conditionally pin rubocop version

Gemfile

@@ -13,7 +13,13 @@ group :tests do
   gem 'rake', '~> 10.0'
   gem 'rspec', '~> 3.0'
   gem 'rubocop-rspec'
-  gem 'rubocop'
+  # rubocop 0.58 throws when testing against ruby 2.1, so pin to the latest,
+  # unless we're dealing with jruby...
+  if RUBY_PLATFORM == 'java'
+    gem 'rubocop'
+  else
+    gem 'rubocop', '0.57.2'
+  end
   gem 'simplecov-console'
   # the test gems required for module testing
   gem 'puppetlabs_spec_helper', '~> 2.7'

README.md

@@ -9,7 +9,7 @@ This is an implementation of the [Resource API](https://github.com/puppetlabs/pu
 
 2. Create a [new module](https://puppet.com/docs/pdk/latest/pdk_generating_modules.html) with the PDK, or work with an existing PDK-enabled module. To create a new module, run `pdk new module <MODULE_NAME>` from the command line, specifying the name of the module. Respond to the dialog questions.
 
-3. To add the the `puppet-resource_api` gem and enable "modern" rspec-style mocking, open the `sync.yml` file in your editor, and add the following content: 
+3. To add the `puppet-resource_api` gem and enable "modern" rspec-style mocking, open the `sync.yml` file in your editor, and add the following content:
 
 ```
 # .sync.yml