Fix vim invocation on Windows

[ms11]

Setting environment variables in the command string itself doesn't work on Windows, but system can accept those variables in a hash as it's first argument. Also, I think this is probably the "more correct" way of setting them, not just simply trusting the shell to handle it.

[notalex]

Thanks for the patch. I will test it out and merge it in a few days.

[parkr]

Line 91 will need to be deleted, or have the env vars removed and used in the execution incantation