Update README.md

Typo in typeMap.length

Author: GouravKumar13

README.md

@@ -699,7 +699,7 @@ Each proposal for an ECMAScript feature goes through the following maturity stag
     console.log(typeMap.get(keyObj));     // object
     console.log(typeMap.get({'one': 1})); // undefined
 
-    console.log(typeMap.size ); // 3
+    console.log(typeMap.size ); // 4
 
     for(let item of typeMap) {
       console.log(item);
@@ -2523,4 +2523,4 @@ Most of these features already supported by some browsers and try out with babel
     console.log(numbers); // [1, 3, 2, 4, 5]
    ```
 
-   **[⬆ Back to Top](#table-of-contents)**
+   **[⬆ Back to Top](#table-of-contents)**