Removes trailing slash on bundle_path

[a-warner]

There seems to be some kind of conflict with bufkill.vim, triggered by doing something like:

• "mvim ." in some project
• :Btabedit somegem
• :bd: or :q or anything that kills the window

This only happens with locally bundled gems, BUNDLE_DISABLE_SHARED_GEMS set, and the BUNDLE_PATH ends with a /, so chop it off if it's there

[a-warner]

There may be some issues with this one...let me do some troubleshooting and get back to you