Fix for fenced code block re in HTML block parser.
Fix for fenced code block re in HTML block parser.

Kapeli/php-markdown,jockchou/php-markdown,filipstefansson/bootstrap-3-shortcodes,queirozfcom/php-markdown-with-syntax-highlight,nazar-pc/php-markdown-next,mariokonrad/php-markdown,filipstefansson/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,itafroma/php-markdown,MWDelaney/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,ashur/php-markdown,n054/php-markdown,robbieaverill/php-markdown