Add alias "m68k" to "Motorola 68K Assembly" (#4683)
Add alias "m68k" to "Motorola 68K Assembly" (#4683)

This allows to use this linguist-language in .gitattributes
as the syntax of that file doesn't allow whitespaces.

See https://github.com/github/linguist/issues/4681
pchaigno/linguist,erkyrath/linguist,sebgod/linguist,erkyrath/linguist,pchaigno/linguist,pchaigno/linguist,github/linguist,sebgod/linguist,github/linguist,pchaigno/linguist,github/linguist,sebgod/linguist,christop/linguist,erkyrath/linguist,github/linguist,erkyrath/linguist,sebgod/linguist,christop/linguist