Use `sh -c` when calling commands

[hauleth]

Not everyone is working with POSIX compatible shell (I am using Fish) and without this plugin is unusable.

[azirbel]

Just ran into this problem too. I was able to work around it with set shell=/bin/bash.

[hauleth]

I do not want to set shell=/bin/bash as I am using NeoVim terminal support which run &shell when started.