Update README.md

I think there is not any reason to assign 2 times.

Author: saroamirkhanyan

README.md

@@ -2165,11 +2165,11 @@ Most of these features already supported by some browsers and try out with babel
     The above logical assignment operation can be expanded to:
 
     ```javascript
-      x = x ?? (x = y);
+      x ?? (x = y);
       (OR)
       if (!x) {
         x = y;
       }
     ```
 
-    **[⬆ Back to Top](#table-of-contents)**
+    **[⬆ Back to Top](#table-of-contents)**