Log Message:
Update ruby-logging to 2.1.0.

== 2.1.0 / 2016-03-13

Enhancements
- appender factories now fail explicitly on bad arguments [PR #117]
- console loggers (stdout, stderr) use `write` for compatibility [PR #127]
- allow whitespace in traced method names [PR #128]
- accessor methods for `backtrace` settings [PR #134]
- asynchronous writing from buffered appenders [PR #135]
- improve date format performance when outputting microseconds [PR #136]
- added some thread safety to log level setters [PR #137]
- use `write` everywhere instead of `syswrite` [PR #138]

Bug Fixes
- fixing encodings in tests [PR #116]
- fix Rails4 logger compatibility [PR #121]
- explicitly adding the MIT license [PR #123]
- update `object_id` format in inspect methods [PR #133]
- fixed Travis-CI tests