warn if no ag installed

Author: JonRowe

Rakefile

@@ -60,6 +60,7 @@ end
 
 desc "Updates the rspec.github.io docs"
 task :update_docs, [:version, :branch, :website_path] do |t, args|
+  abort "You must have ag installed to generate docs" if `which ag` == ""
   args.with_defaults(:website_path => "../rspec.github.io")
   run_command "git checkout #{args[:branch]} && git pull --rebase"
   each_project :except => UnDocumentedProjects do |project|