chore(ci): add GitHub Actions

Author: yoshinorin

.github/workflows/ci.yaml

@@ -0,0 +1,28 @@
+name: build
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [11]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Cache
+      uses: actions/cache@v2
+      env:
+        cache-name: cache-sbt-libs
+      with:
+        path: |
+          ~/.ivy2/cache
+          ~/.sbt
+          ~/.cache/coursier/v1
+        key: build-${{ env.cache-name }}-${{ hashFiles('build.sbt') }}
+    - name: Set up JDK
+      uses: actions/setup-java@v1
+      with:
+        java-version: ${{ matrix.java }}
+    - name: Build executable
+      run: sbt package