0.5.2

Install/upgrade instructions here.

• Added a --no-cache option to fig build, which bypasses the cache just like docker build --no-cache.
• Fixed the dns: fig.yml option, which was causing fig to error out.
• Fixed a bug where fig couldn't start under Python 2.6.
• Fixed a log-streaming bug that occasionally caused fig to exit.

Thanks @dnephin and @marksteve!