corrected typos and updated URL paths for RESTCONF in module03 hello_…

[stevehwinwood]

Hello,

I'm learning Python for network automation and the DevNet labs are a great resource!

For me the hello_lab.py script didn't work for RESTCONF and I had to update the api URL in the check_restconf function. I also spotted a few typos and corrected them, and all these changes are reflected in this pull request.

I hope you find this useful.

Steve