added rake version to Gemfile
added rake version to Gemfile

cristianonicolai/jbpm-website,droolsjbpm/jbpm-website,cristianonicolai/jbpm-website,droolsjbpm/jbpm-website,cristianonicolai/jbpm-website,droolsjbpm/jbpm-website,droolsjbpm/jbpm-website,cristianonicolai/jbpm-website