Migrate CI from Travis to GitHub Actions, adding recommended Elixir a…

…nd Erlang/OTP combinations (#112)

.github/workflows/ci.yml

@@ -0,0 +1,61 @@
+name: Elixir CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  mix_test:
+    name: mix test (Elixir ${{matrix.elixir}} | OTP ${{matrix.otp}})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - elixir: 1.4.x
+            otp: 18.3.4.11
+          - elixir: 1.5.x
+            otp: 18.3.4.11
+          - elixir: 1.6.x
+            otp: 19.3.6.13
+          - elixir: 1.7.x
+            otp: 19.3.6.13
+          - elixir: 1.8.x
+            otp: 20.3.8.26
+          - elixir: 1.9.x
+            otp: 20.3.8.26
+            warnings_as_errors: true # 1.10 is not enough as its --warnigs-as-errors has bugs https://github.com/elixir-lang/elixir/issues/10073
+          - elixir: 1.10.x
+            otp: 21.3.8.17
+          - elixir: 1.10.x
+            otp: 23.0.3
+            warnings_as_errors: true
+            static_analysis: true
+    env:
+      MIX_ENV: test
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-elixir@v1
+        with:
+          otp-version: ${{matrix.otp}}
+          elixir-version: ${{matrix.elixir}}
+      - name: Install Dependencies
+        run: |
+          mix local.hex --force
+          mix local.rebar --force
+          mix deps.get --only test
+      - name: Cache build artifacts
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.hex
+            ~/.mix
+            _build
+          key: ${{ matrix.otp }}-${{ matrix.elixir }}-build
+      - run: mix compile --warnings-as-errors
+        if: matrix.warnings_as_errors
+      - run: mix test
+      - run: mix dialyzer --halt-exit-status
+        if: matrix.static_analysis