chore(demo): upgrade monaco editor to 0.20.0

Author: urish

demo/src/index.html

@@ -27,7 +27,7 @@ <h2>AVR8js LED Demo</h2>
         <pre id="serial-output-text"></pre>
       </div>
     </div>
-    <script src="//cdnjs.cloudflare.com/ajax/libs/monaco-editor/0.18.0/min/vs/loader.js"></script>
+    <script src="//cdnjs.cloudflare.com/ajax/libs/monaco-editor/0.20.0/min/vs/loader.js"></script>
     <script src="./index.ts"></script>
   </body>
 </html>

demo/src/index.ts

@@ -29,7 +29,7 @@ void loop() {
 declare const window: any; // eslint-disable-line @typescript-eslint/no-explicit-any
 declare const monaco: any; // eslint-disable-line @typescript-eslint/no-explicit-any
 window.require.config({
-  paths: { vs: 'https://cdnjs.cloudflare.com/ajax/libs/monaco-editor/0.18.0/min/vs' }
+  paths: { vs: 'https://cdnjs.cloudflare.com/ajax/libs/monaco-editor/0.20.0/min/vs' }
 });
 window.require(['vs/editor/editor.main'], () => {
   editor = monaco.editor.create(document.querySelector('.code-editor'), {