Support windows (cmd.exe)

[SuperCuber]

The command generation in this part of the code:

vim-jack-in/autoload/jack_in.vim

Line 46 in 7fed796

let l:dep_vector = printf('''[%s "%s"]''', dep, inj['version'])

uses single quotes which don't properly work on Windows.

I only tried :Lein, but a successful command for Windows looks like:

lein update-in :dependencies conj "[refactor-nrepl/refactor-nrepl \"3.6.0\"]" -- update-in :repl-options:nrepl-middleware conj refactor-nrepl.middleware/wrap-refactor -- update-in :plugins conj "[cider/cider-nrepl \"0.30.0\"]" -- repl

I think this command should also work on unix shells.

I would make a PR but I definitely do not know my way around vimscript well enough 🙃 for now I'll hard-code this into my config