docs(readme): fix anchor links in README.md (#3436)

Author: akiomik

README.md

@@ -33,14 +33,14 @@ visit our [code samples repo](https://github.com/aws-samples/aws-sdk-js-tests).
    1. [Modularized packages](#modularized-packages)
    1. [API consistency changes](#api-changes)
       1. [Configuration](#configuration)
-      1. [Middleware Stack](#Middleware)
+      1. [Middleware Stack](#middleware)
    1. [How to upgrade](#other-changes)
 1. [High Level Concepts in V3](#high-level-concepts)
    1. [Generated Packages](#generated-code)
    1. [Paginators](#paginators)
    1. [Abort Controller](#abort-controller)
    1. [Middleware Stack](#middleware-stack)
-1. [Install from Source](#install-from-Source)
+1. [Install from Source](#install-from-source)
 1. [Giving feedback and contributing](#giving-feedback-and-contributing)
 1. [Known Issues](#known-issues)