Alphabetise all keywords in yang lexer (#1428)
Alphabetise all keywords in yang lexer (#1428)

* Alphabetise all keywords in yang lexer

* fix typo in keyword of yang lexer
dscorbett/pygments,pygments/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments