Bump src/collector

Bump cloudfoundry/collector:
  John Tuley:
     Remove unused received_requests metric from router handler ( Travis Success: https://travis-ci.org/cloudfoundry/collector/builds/29610980 )
     Do not send metrics with no value [#74567060] ( Travis Success: https://travis-ci.org/cloudfoundry/collector/builds/29609392 )

Signed-off-by: John Tuley <jtuley@pivotallabs.com>