Markdown: decode single quotes in fenced code blocks

Props @synapticism
See Automattic#403

_inc/lib/markdown/gfm.php

@@ -167,7 +167,7 @@ public function codeblock_restore( $text ) {
 	 * @return string         Codeblock with unescaped interior
 	 */
 	public function do_codeblock_restore( $matches ) {
-		$block = html_entity_decode( $matches[3] );
+		$block = html_entity_decode( $matches[3], ENT_QUOTES );
 		$open = $matches[1] . $matches[2] . "\n";
 		return $open . $block . $matches[4];
 	}