suppress false positives in ufuzz (#4419)

README.md

@@ -1217,3 +1217,13 @@ To allow for better optimizations, the compiler makes various assumptions:
   // SyntaxError: Identifier 'a' has already been declared
   ```
   UglifyJS may modify the input which in turn may suppress those errors.
+- Later versions of JavaScript will throw `SyntaxError` with the following:
+  ```js
+  try {
+    // ...
+  } catch ({ message: a }) {
+    var a;
+  }
+  // SyntaxError: Identifier 'a' has already been declared
+  ```
+  UglifyJS may modify the input which in turn may suppress those errors.