Two small fixes: spelling & broken link

Challenges/Challenge1.md

@@ -1,6 +1,6 @@
 # Using predefined container configurations
 ## Background
-In order to learn about configuring development containers, it is helpful to start with the simplist definition.  The simplist .devcontainer/devcontainer.json file has only an image entry.  
+In order to learn about configuring development containers, it is helpful to start with the simplest definition.  The simplest .devcontainer/devcontainer.json file has only an image entry.
 ```json
 {
     "image": "python:3.9"

Challenges/Challenge5.md

@@ -8,7 +8,7 @@ One of the options is to configure the extensions that are installed in the code
 Beyond the devcontainer.json, it is possible to install extensions that are installed locally in Visual Studio Code in the remote container.  This can be done via the Extensions tab.
 
 ### Rest Client - a helpful extension
-There is an extension that is very helpful when developing REST APIs.  It is the [Rest Client](https://marketplace.visualstudio.com/items?itemName=humao).  Among other things, it allows you to send HTTP requests from a file (*.http) and see the results in a separate panel.  See the example below:
+There is an extension that is very helpful when developing REST APIs.  It is the [Rest Client](https://marketplace.visualstudio.com/items?itemName=humao.rest-client).  Among other things, it allows you to send HTTP requests from a file (*.http) and see the results in a separate panel.  See the example below:
 ![Rest Client Extension](../Images/RestClientExtension.png)
 
 ## Challenge