docs(README.md): update docs to match new version
docs(README.md): update docs to match new version

yaniswang/showdown,bsnizek/showdown,showdownjs/showdown,NichenLg/showdown,juanonsoftware/showdown,stevemao/showdown,axter/showdown,digideskio/showdown,phw/showdown,juanonsoftware/showdown,digideskio/showdown,alazyer/showdown,coolroad/showdown,OMGgogong/showdown,OMGgogong/showdown,webutilz/showdown,webutilz/showdown,bsnizek/showdown,yaniswang/showdown,phw/showdown,axter/showdown,showdownjs/showdown,pazof/showdown,snegovick/showdown,snegovick/showdown,xinshitn/showdown,pazof/showdown,stevemao/showdown,coolroad/showdown,NichenLg/showdown,alazyer/showdown,twitwi/showdown,xinshitn/showdown,twitwi/showdown