fish.kak: fix highlighting for single quoted strings
fish.kak: fix highlighting for single quoted strings

fish allows to escape single quotes within single quoted strings,
just like double quotes in double quoted strings.

https://fishshell.com/docs/current/index.html#quotes

danr/kakoune,danr/kakoune,Somasis/kakoune,lenormf/kakoune,mawww/kakoune,Somasis/kakoune,Somasis/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,mawww/kakoune,alexherbo2/kakoune,lenormf/kakoune,Somasis/kakoune,danr/kakoune,casimir/kakoune,casimir/kakoune,lenormf/kakoune,casimir/kakoune,casimir/kakoune,mawww/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,mawww/kakoune,lenormf/kakoune,danr/kakoune