fvm Support

[tobinharris]

Hi!

Nice plug. Would it be difficult to add fvm support so that vim-flutter uses that if detected?

[thosakwe]

Try let g:flutter_command = 'fvm' in your vimrc.

[3to8-decoder]

setting it to 'fvm' doesn't work, it should be 'flutter fvm'

however, current code does not support g:flutter_command with spaces in it.
Very easy to change though. I fixed it in a fork.
See merge request: #45