Add path support for the fish shell

[dnicolson]

This pull request fixes an issue with the fish shell when determining the system path, the following error would appear in the console:

Traceback (most recent call last):
  File "/Users/dave/Library/Application Support/Sublime Text 3/Packages/JavaScript Enhancements/main.py", line 140, in fixPath
    currSysPath = getSysPath()
  File "/Users/dave/Library/Application Support/Sublime Text 3/Packages/JavaScript Enhancements/main.py", line 129, in getSysPath
    sysPath = sysPath.splitlines()[-1]
IndexError: list index out of range

Prepending the command with the env command fixes the issue, it has been tested with the fish, zsh and bash shells.

[pichillilorenzo]

Ok! Thanks!