Fix excerpt on new PHP 5.4

excerpt() on some newer versions of PHP 5.4 includes a space in the <br />.
Accomodate that and strip that value as well.

src/Error/Debugger.php

@@ -435,7 +435,7 @@ class Debugger {
 		$highlight = highlight_string($str, true);
 		if ($added) {
 			$highlight = str_replace(
-				'&lt;?php&nbsp;<br/>',
+				['&lt;?php&nbsp;<br/>', '&lt;?php&nbsp;<br />'],
 				'',
 				$highlight
 			);