Bump src/gorouter

Bump :
  John Tuley and Zach Robinson:
     Merge remote-tracking branch origin/pr/58
     Merge remote-tracking branch origin/pr/56
  Andrew Poydence:
     Fixed instrumentation bug related to dropsonde-instance-id
  Chris Piraino, Julian Friedman and Luan Santos:
     Update to use the thinner yagnats interface
  Johannes Petzold:
     merge from master
  Warren Fernandes:
     remove loggregatorlib dependencies
     use dropsonde for logging