Add support for #!/usr/bin/env bash for .vimrc (DetectBash)

[gonzaru]

Hello!

As some of scripts of the repo uses this path, maybe it's a good idea also support it on .vimrc if necessary.

fun! s:DetectBash()
    if getline(1) == '#!/usr/bin/bash' || getline(1) == '#!/bin/bash' || getline(1) == '#!/usr/bin/env bash'
      ...
    endif
endfun

Regards!