Switch from Travis CI to GitHub Actions

.github/workflows/ci.yml

@@ -0,0 +1,14 @@
+name: CI
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js 14 LTS
+        uses: actions/setup-node@v1
+        with:
+          node-version: 14.x
+      - run: npm install -g gulp-cli
+      - run: npm install
+      - run: npm test

.travis.yml

@@ -1,10 +0,0 @@
-language: node_js
-node_js:
-  - lts/*
-cache:
-  directories:
-    - node_modules
-install:
-  - npm install -g npm@latest
-  - npm install -g gulp-cli
-  - npm install