Wrong resources navigation on menu fixed (mbeaudru#64)

Author: iifeoluwa

readme.md

@@ -57,7 +57,7 @@ When you struggle to understand a notion, I suggest you look for answers on the
         * [Array.prototype.map()](#arrayprototypemap)
         * [Array.prototype.filter()](#arrayprototypefilter)
         * [Array.prototype.reduce()](#arrayprototypereduce)
-      - [External Resource](#external-resource)
+      - [External Resource](#external-resource-2)
     + [Spread operator "..."](#spread-operator-)
       - [Sample code](#sample-code-3)
       - [Explanation](#explanation-1)
@@ -73,28 +73,27 @@ When you struggle to understand a notion, I suggest you look for answers on the
       - [Explanation](#explanation-3)
         * [Create the promise](#create-the-promise)
         * [Promise handlers usage](#promise-handlers-usage)
-      - [External Resources](#external-resources)
+      - [External Resources](#external-resources-2)
     + [Template literals](#template-literals)
       - [Sample code](#sample-code-5)
-      - [External resources](#external-resources-2)
+      - [External resources](#external-resources-3)
     + [Tagged Template Literals](#tagged-template-literals)
       - [External resources](#external-resources-4)
     + [Imports / Exports](#imports--exports)
       - [Explanation with sample code](#explanation-with-sample-code-1)
         * [Named exports](#named-exports)
         * [Default import / export](#default-import--export)
-      - [External resources](#external-resources-3)
+      - [External resources](#external-resources-5)
     + [JavaScript *this*](#-javascript-this)
-      - [External resources](#external-resources-4)
+      - [External resources](#external-resources-6)
     + [Class](#class)
       - [Samples](#samples)
-      - [External resources](#external-resources-5)
+      - [External resources](#external-resources-7)
     + [Async Await](#async-await)
       - [Sample code](#sample-code-6)
       - [Explanation with sample code](#explanation-with-sample-code-2)
-      - [External resources](#external-resources-6)
+      - [External resources](#external-resources-8)
     + [Truthy / Falsy](#truthy--falsy)
-      - [External resources](#external-resources-7)
     + [Static Methods](#static-methods)
       - [Short Explanation](#short-explanation-1)
       - [Sample Code](#sample-code-7)