Parser: Remove misplaced + in regular expression

This was a mistake in Ie994059. I experimented with different
patterns and apparently forgot to remove this. It doesn't make sense
here. The keys are numeric and can't contain a "+" character (but a
"-" in case the namespace is negative).

Change-Id: Ifdf22405c5ba9f300bed2a4e65ac487e64485f28

includes/parser/LinkHolderArray.php

@@ -268,7 +268,7 @@ class LinkHolderArray {
 
 		# Do the thing
 		$text = preg_replace_callback(
-			'/<!--LINK\'" (-?[\d+:]+)-->/',
+			'/<!--LINK\'" (-?[\d:]+)-->/',
 			static function ( array $matches ) use ( $replacePairs ) {
 				return $replacePairs[$matches[1]];
 			},