add python3.5 support

Author: yosupo06

.github/workflows/expander.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python-version: [3.6]
+        python-version: [3.5, 3.6]
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}