Removed "next" branch mention from CONTRIBUTING.md
Removed "next" branch mention from CONTRIBUTING.md

GLS isn't active enough to need that overhead yet.
HighSchoolHacking/GLS,general-language-syntax/GLS,HighSchoolHacking/GLS,chris-j-tang/GLS,chris-j-tang/GLS,chris-j-tang/GLS,general-language-syntax/GLS,chris-j-tang/GLS,chris-j-tang/GLS,chris-j-tang/GLS,HighSchoolHacking/GLS,HighSchoolHacking/GLS,general-language-syntax/GLS,general-language-syntax/GLS,general-language-syntax/GLS,HighSchoolHacking/GLS,general-language-syntax/GLS,HighSchoolHacking/GLS