Make package build use python 3.7

Author: chrisjsewell

.github/workflows/tests.yml

@@ -60,14 +60,18 @@ jobs:
     if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags')
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout source
-        uses: actions/checkout@v2
-      - name: Build package
-        run: |
-          pip install wheel
-          python setup.py sdist bdist_wheel
-      - name: Publish
-        uses: pypa/gh-action-pypi-publish@v1.1.0
-        with:
-          user: __token__
-          password: ${{ secrets.PYPI_KEY }}
+    - name: Checkout source
+      uses: actions/checkout@v2
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Build package
+      run: |
+        pip install wheel
+        python setup.py sdist bdist_wheel
+    - name: Publish
+      uses: pypa/gh-action-pypi-publish@v1.1.0
+      with:
+        user: __token__
+        password: ${{ secrets.PYPI_KEY }}