Windows network locations should be supported

[Heptite]

Under windows when I try to open a network share with //machine.name/path/ I get the error:

The "path" must be an absolute path but "\\machine.name\path\" has specfied

[lambdalisue]

https://github.com/lambdalisue/fern.vim/wiki/Supported-platforms

Unfortunately, fern does not UNC path. PR is welcome.