Update package versions.

Do not use Path in schemas (causes issues with empty paths).
Change how notifications are handled.
Run tests with Python 3.9

.github/workflows/testing.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.6, 3.7, 3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v2