Update iTerm script

iTerm2 made some changes to its scripting, which causes 'got' to silently fail when using iTerm2, and setting
let g:gtfo#terminals = { 'mac' : 'iterm' }

Here is the new scripting commands:
https://github.com/gnachman/iTerm2/blob/master/iTerm2.sdef

Perhaps it might be necessary to check and have separate scripts  for iTerm/iTerm2.
Thoughts?
Need a line above this for the empty case, similar to line 144:

    if s:empty(s:termpath) | let s:termpath = 'iTerm.app' | endif