Initial github actions config. (#23)

Confgure GitHub Actions CI as travis-ci.org is going away and there's no compelling reason to migrate to travis-ci.com.
diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
new file mode 100644
index 0000000..ace9f1e
--- /dev/null
+++ b/.github/workflows/python-package.yml
@@ -0,0 +1,31 @@
+# This workflow will install Python dependencies, run tests and lint with a variety of Python versions
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
+
+name: Python Portpicker & Portserver
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: [3.6, 3.7, 3.8, 3.9]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pytest tox
+          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+      - name: Test with tox
+        run: |
+          # Run tox using the version of Python in `PATH`
+          tox -e py