Pin puppetlabs_spec_helper to 0.8.0

0.8.1 has broken the 'rake lint' task which checks for style violations.
Unfortunately this means some have snuck in so this will break the build.

Revert when on merge of puppetlabs/puppetlabs_spec_helper#78

Gemfile

@@ -5,7 +5,7 @@ group :test do
 end
 
 group :rake, :test do
-  gem 'puppetlabs_spec_helper',  :require => false
+  gem 'puppetlabs_spec_helper', '0.8.0',  :require => false
   gem 'puppet-blacksmith',       :require => false
   gem 'rspec-system-puppet',     :require => false
 end