extra code to handle ZSH completion issues after unloading RVM, fix #1835
Use `\rm -f` instead of `rm` when removing zsh comp dump file to bypass any alias of rm in user's zsh configuration.
Merge pull request #1837 from JoeKun/master

Use `\rm -f` instead of `rm` when removing zsh comp dump file to bypass any alias of rm in user's zsh configuration.