bump chruby to 0.3.7

0.3.7 / 2013-08-18

Multiple style changes and optimizations. (@zendeavor)
Safely glob the contents of /opt/rubies and ~/.rubies. This prevents nullglob errors under zsh and .rbx directories from being added to RUBIES.
Unset GEM_PATH in chruby_reset if it has become empty. Allows the RubyGems to use the default GEM_PATH.
Safely quote RUBIES[@] to prevent implicit word-splitting when listing RUBIES.
Map -V to --version in chruby. (@havenwood)
Added benchmarks.