Bump jruby version to 1.7.2.
Explicitly run chruby-exec under bash to avoid dash.
Also specify -i so .zshrc is loaded.
Remove the #! so that chruby-exec runs under the current shell.
Revert "Remove the #! so that chruby-exec runs under the current shell."

This reverts commit 8fb0481b59390182cc6025b8e4060b59d7bb4f1c.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Revert "Remove the #! so that chruby-exec runs under the current shell."
  Remove the #! so that chruby-exec runs under the current shell.
  Also specify -i so .zshrc is loaded.
  Explicitly run chruby-exec under bash to avoid dash.
  Bump jruby version to 1.7.2.