Fix a typo

Author: mpdude

src/Runtime/EscaperRuntime.php

@@ -267,7 +267,7 @@ public function escape($string, string $strategy = 'html', ?string $charset = nu
 
                 $regex = match ($strategy) {
                     'html_attr' => '#[^a-zA-Z0-9,\.\-_]#Su',
-                    'html_attr_relaxed' => '#[^a-zA-Z0-9,\._:@\[\]]#Su',
+                    'html_attr_relaxed' => '#[^a-zA-Z0-9,\.\-_:@\[\]]#Su',
                 };
 
                 $string = preg_replace_callback($regex, function ($matches) {