Fix typo

Thanks @DeepDiver1975

lib/base.php

@@ -215,7 +215,7 @@ class OC {
 
 	/*
 	* This function adds some security related headers to all requests served via base.php
-	* The implementation of this function as hto happen here to ensure that all third-party 
+	* The implementation of this function has to happen here to ensure that all third-party 
 	* components (e.g. SabreDAV) also benefit from this headers.
 	*/
 	public static function addSecurityHeaders() {