Release 2.6.3.0

This patch releases fixes a number of smaller issues:

* the gem will no longer start traces on static assets (https://github.com/appneta/oboe-ruby/pull/31)
* fix occasionally broken `profile_name` values when using [custom method tracing](https://github.com/appneta/oboe-ruby#tracing-methods)
* fix for incorrectly starting traces when in `through` tracing mode under certain circumstances
* Expand the test suite to validate sample rates and tracing modes (https://github.com/appneta/oboe-ruby/pull/8)