(maint) pin beaker for ruby 1.8.7

Travis is failing on 1.8.7 due to some recent updates in rails. This should fix
the issue.

.travis.yml

@@ -1,5 +1,6 @@
 ---
 language: ruby
+bundler_args: --without system_tests
 script: "bundle exec rake spec SPEC_OPTS='--format documentation'"
 after_success:
   - git clone -q git://github.com/puppetlabs/ghpublisher.git .forge-release

Gemfile

@@ -3,13 +3,16 @@ source ENV['GEM_SOURCE'] || "https://rubygems.org"
 group :development, :test do
   gem 'rake'
   gem 'puppetlabs_spec_helper', :require => false
-  gem 'beaker',                 :require => false
-  gem 'beaker-rspec',           :require => false
-  gem 'serverspec',             :require => false
   gem 'rspec-puppet', '~> 1.0'
   gem 'puppet-lint',  '~> 1.1'
 end
 
+group :system_tests do
+  gem 'beaker',                :require => false
+  gem 'beaker-rspec',          :require => false
+  gem 'serverspec',            :require => false
+end
+
 if puppetversion = ENV['PUPPET_GEM_VERSION']
   gem 'puppet', puppetversion, :require => false
 else