readme - fix link

Author: gavinr

Diff for: README.md

@@ -39,6 +39,6 @@ Run `grunt` and as you modify your files, the web app (in the `dist` folder - se
 
 A few notes about the general ideas and principles that are used in both the `builder` and `developer` versions of this code
 
-- We are currently supporting [TypeScript version 3.9](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html).
+- We are currently supporting [TypeScript version 3.9](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-9.html).
 - The Declare Decorator is used to tell TypeScript how to translate our Widget class into a dojo/declare syntax that Web AppBuilder is looking for. [Decorators are currently experimental](https://www.typescriptlang.org/docs/handbook/decorators.html) (although widely used) so beware of that small risk. If TypeScript did take out decorators at some point, we would have to change how we're doing this.
 - For more info, see this blog post: [Custom Web AppBuilder Widgets in TypeScript ](https://community.esri.com/people/GRehkemper-esristaff/blog/2017/12/13/custom-web-appbuilder-widgets-in-typescript)