Fix doc-getstarted.md using wrong url for MXML Namespace

The ns only works when using http, using https causes the compiler to throw an error.
Seems this was an oversight when performing the CMS Migration that slipped under the cracks as this change is listed in `content/migration/changes.txt`.

Author: Fancy2209

content/doc-getstarted.md

@@ -82,7 +82,7 @@ This is a very simple, generic hello world application.  You can learn a lot mor
 The complete code listing is (there may be some variations, depending on your IDE template. Just make sure what we talked about above match) :
 
     <?xml version="1.0" encoding="utf-8"?>
-    <s:Application xmlns:fx="https://ns.adobe.com/mxml/2009"
+    <s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
                    xmlns:s="library://ns.adobe.com/flex/spark"
                    xmlns:mx="library://ns.adobe.com/flex/mx" width="640" height="480">
 
@@ -116,4 +116,4 @@ The complete code listing is (there may be some variations, depending on your ID
  [12]: https://vimeo.com/46898669
  [13]: https://fdt.powerflasher.com/
  [14]: https://blogs.apache.org/flex/
- [15]: doc/flex/using/index.html
+ [15]: doc/flex/using/index.html