Clean ie_proxypac

Hi @bmerinofe,

This pull request tries to clean https://github.com/rapid7/metasploit-framework/pull/2719 by updating the branch, since looks like you started to work from a out of date branch (it's a always a good idea to sync your repo with the r7 one before starting a new working branch to keep things more up to date :))

But indeed the only thing this pull request should update is modules/post/windows/manage/ie_proxypac.rb. Please check which the module working is still what you intended and you feel comfortable with the changes. Once you are, feel free to land this pull request into your repo and https://github.com/rapid7/metasploit-framework/pull/2719 should be ready to go :) On the other hand don't hesitate to ask if there is any doubt on your side!

Thanks!