Switch from travis-ci to github actions

Author: syohex

.github/workflows/test.yml

@@ -0,0 +1,24 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        emacs_version:
+          - 25.1
+          - 26.3
+          - 27.1
+          - snapshot
+    steps:
+    - uses: purcell/setup-emacs@master
+      with:
+        version: ${{ matrix.emacs_version }}
+    - uses: actions/checkout@v1
+    - name: Run tests
+      run: |
+        make test