scheme.kak: fixes for r7rs word characters
scheme.kak: fixes for r7rs word characters

Was missing _ and @ in various places.

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