Add python 3.9 to tests and compatibility

- Bump github action versions
- Add PyPy and Python 3.9 to github tests
- Update pipfile.lock (typed-ast 1.4.0 fails in CI)

Author: calebj

.github/workflows/tests.yaml

@@ -6,11 +6,11 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [3.8, 3.7, 3.6]
+        python-version: [3.9, 3.8, 3.7, 3.6, 'pypy-3.6', 'pypy-3.7']
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: 'Set up Python ${{ matrix.python-version }}'
-      uses: actions/setup-python@v1
+      uses: actions/setup-python@v2
       with:
         python-version: '${{ matrix.python-version }}'
     - name: 'Install Python packaging tools'