Fix GitHub link in footer (#255)

Author: berekuk

website/core/Footer.js

@@ -50,7 +50,7 @@ class Footer extends React.Component {
           </div>
           <div>
             <h5>More</h5>
-            <a href="https://github.com/reduxjs/redux/">GitHub</a>
+            <a href="https://github.com/reduxjs/redux-toolkit">GitHub</a>
             <a
               className="github-button"
               href={this.props.config.repoUrl}