Fixed small error in emphasis parser.
Fixed small error in emphasis parser.

robbieaverill/php-markdown,itafroma/php-markdown,mariokonrad/php-markdown,ashur/php-markdown,alganet/ElephantMarkdown,Kapeli/php-markdown,queirozfcom/php-markdown-with-syntax-highlight,MWDelaney/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes,c9s/php-markdown,filipstefansson/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,nazar-pc/php-markdown-next,n054/php-markdown,jockchou/php-markdown,MWDelaney/bootstrap-3-shortcodes,drosenstark/php-markdown,TypeFriendly/PHP-Markdown