Bump src/collector

Bump cloudfoundry/collector:
  Tim Labeeuw:
     Updated the nats gem to the newest beta to match all other components ( Travis Success: https://travis-ci.org/cloudfoundry/collector/builds/14324506 )
     Update rspec, timecop and ci_reporter ( Travis Unknown )
  Matthew McNew:
     add new cf metrics plugin for collector ( Travis Success: https://travis-ci.org/cloudfoundry/collector/builds/13832760 )