depend on rubocop-rspec lower than 1.6

Gemfile

@@ -26,7 +26,7 @@ group :test do
   gem 'puppet-blacksmith',                                          require: false
   gem 'voxpupuli-release',                                          require: false, git: 'https://github.com/voxpupuli/voxpupuli-release-gem.git'
   gem 'puppet-strings',                                             require: false, git: 'https://github.com/puppetlabs/puppetlabs-strings.git'
-  gem 'rubocop-rspec', '~> 1.5',                                    require: false if RUBY_VERSION >= '2.0.0'
+  gem 'rubocop-rspec', '< 1.6', '~> 1.5',                           require: false if RUBY_VERSION >= '2.0.0'
   gem 'json_pure', '<= 2.0.1',                                      require: false if RUBY_VERSION < '2.0.0'
   gem 'ipaddress',                                                  require: false
   gem 'rspec-its',                                                  require: false