Replace travis with GitHub Actions

Author: dcroote

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+name: CI
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        toolchain: [stable]
+        target: [armv7-unknown-linux-gnueabihf, arm-unknown-linux-gnueabihf, aarch64-unknown-linux-gnu]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.toolchain }}
+          target: ${{ matrix.target }}
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          use-cross: true
+          command: build
+          args: --target ${{ matrix.target }}