fix rake

avoid failure with

rake aborted!
NoMethodError: undefined method `last_comment' for #<Rake::Application:0x00560bba531620>

Author: TheMeier

Gemfile

@@ -1,6 +1,7 @@
 source "https://rubygems.org"
 
-gem 'rspec', '~> 3.1.0'
+gem 'rspec'
+gem 'rake'
 gem 'puppetlabs_spec_helper'
 if puppetversion = ENV['PUPPET_GEM_VERSION']
   gem 'puppet', puppetversion,  :require => false