[js] use native String.trim when -D js-es5

std/StringTools.hx

@@ -244,11 +244,13 @@ class StringTools {
 
 		This is a convenience function for `ltrim(rtrim(s))`.
 	**/
-	public #if (cs || java) inline #end static function trim( s : String ) : String {
+	public #if (cs || java || (js && js_es5)) inline #end static function trim( s : String ) : String {
 		#if cs
 		return untyped s.Trim();
 		#elseif java
 		return untyped s.trim();
+		#elseif (js && js_es5)
+		return untyped s.trim();
 		#else
 		return ltrim(rtrim(s));
 		#end