Relax reNative as it's limited in scope.

dist/lodash.underscore.js

@@ -206,7 +206,7 @@
   var reNative = RegExp('^' +
     String(toString)
       .replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
-      .replace(/\b(function)\b.*?(?=\\\()| for .+?(?=\\\])|\btoString\b/g, '$1.*?') + '$'
+      .replace(/toString|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$'
   );
 
   /** Native method shortcuts */