add Sheng Yun in AUTHORS.txt
add Sheng Yun in AUTHORS.txt

davidhalter/jedi-vim,wilywampa/jedi-vim,pze/jedi-vim,genzj/jedi-vim,clavery/jedi-vim,blueyed/jedi-vim,FBruynbroeck/jedi-vim,itchyny/jedi-vim,sethfowler/pygmalion-vim,aliev/jedi-vim,jmartiuk5/jedi-vim,maxamillion/jedi-vim