Add python3.7 to GitHub action

Author: mpgn

.github/workflows/crackmapexec.yml

@@ -18,7 +18,7 @@ jobs:
     - name: CrackMapExec tests on ${{ matrix.os }}
       uses: actions/setup-python@v1
       with:
-        python-version: 3.8
+        python-version: [3.7, 3.8]
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip