EASY: make Function.prototype.caller/arguments configurable

Summary:
They were mistakenly left as non-configurable, even though the spec says
that they should be in `AddRestrictedFunctionProperties`.

Reviewed By: avp

Differential Revision: D67366247

fbshipit-source-id: 998456a7fa5bc1bdb686751c4fc24177074eebf6

Author: Tzvetan Mikov

lib/VM/JSLib/Function.cpp

@@ -93,7 +93,7 @@ Handle<NativeConstructor> createFunctionConstructor(Runtime &runtime) {
   PropertyFlags pf;
   pf.clear();
   pf.enumerable = 0;
-  pf.configurable = 0;
+  pf.configurable = 1;
   pf.accessor = 1;
   auto res = JSObject::defineNewOwnProperty(
       functionPrototype,