Update ruby to 2.1.5 in blobs.yml
Update ruby to 2.1.5 in blobs.yml

datianshi/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,datianshi/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,datianshi/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,datianshi/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release