Fix argument handling in gh-path helper.
Fix argument handling in gh-path helper.

No Issue
- Make helper behave as stated in description when variable
  number of arguments are passed in.
- Handle leading and trailing slashes when creating output
  url partial.

kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,TryGhost/Ghost-Admin,JohnONolan/Ghost-Admin,acburdine/Ghost-Admin,airycanon/Ghost-Admin,acburdine/Ghost-Admin,kevinansfield/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin