Finagle Metrics Versions Save

Update all dependencies, sbt and its plugins to their latest versions. Thanks to @pmatpadi

Synchronize on the MetricRegistry when registering gauges. Thanks to @bryanv and @ncreep.

• Update to the latest finagle version Thanks to @schrepfler

Fix a possible race condition when adding/removing gauge. Thanks to @samhendley

This release brings Scala 2.12 support. As for 0.0.8, finagle-metrics is cross-published for both 2.11 and 2.12.

• Update to the latest finagle version
• Change project to use the scala 2.12.1

Remove coverage command from travis

Remove the following plugins due to bugs in projects using this lib:

• sbt-scoverage
• sbt-coveralls

• Update to the latest finagle version
• Update to the latest metrics version
• Update to the latest scalatest version
• Update to the latest sbt version
• Change project to use JDK8

Fix exception when adding a preexistent gauge