fix(external-api/middleware): invalid toString call

The intention was to override 'this' argument of 'Error.toString'.

react/features/mobile/external-api/middleware.js

@@ -83,7 +83,7 @@ function _toErrorString(
         error
             ? typeof error === 'string'
                 ? error
-                : Error.prototype.toString(error)
+                : Error.prototype.toString.apply(error)
             : '');
 }