Colorize fish-shell files with a shebang

[CamilleScholtz]

See: #2713

The vast majority if scripts in this repo are fish scripts, however it only shows "shell" in the bar: https://github.com/onodera-punpun/bin

Another example: https://github.com/onodera-punpun/neet
it only shows Makefile in the language bar, yet the fish script is much much bigger and doesn't get shown at all...

All of them are executable.

[arfon]

#2995 fixes this.

The vast majority if scripts in this repo are fish scripts, however it only shows "shell" in the bar: https://github.com/onodera-punpun/bin

The language bar will still list Shell for the same reason outlined here: #2978 (comment) . The files will be highlighted though after #2995 goes into production.