replace Travis CI with Github Actions

Author: dmitmel

.github/workflows/ci.yaml

@@ -0,0 +1,46 @@
+name: CI
+on: [push, pull_request, workflow_dispatch]
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: '15.x'
+
+      - name: Get Yarn cache dir
+        id: yarn-cache-dir
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - uses: actions/cache@v2
+        with:
+          path: ${{ steps.yarn-cache-dir.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-yarn-
+
+      - name: Download ultimate-crosscode-typedefs
+        uses: actions/checkout@v2
+        with:
+          repository: dmitmel/ultimate-crosscode-typedefs
+          path: ultimate-crosscode-typedefs
+      - name: Set up ultimate-crosscode-typedefs
+        working-directory: ultimate-crosscode-typedefs
+        run: |
+          yarn install --production --no-lockfile
+          yarn link
+
+      - name: Install dependencies
+        run: |
+          yarn link ultimate-crosscode-typedefs
+          yarn install --frozen-lockfile
+
+      - name: Build
+        run: yarn run build
+      - name: Lint
+        run: yarn run lint
+      - name: Check formatting
+        run: yarn run check-fmt