Add linting to TravisCI config

Author: Peter Hegman

.travis.yml

@@ -1,7 +1,9 @@
 language: node_js
 node_js:
   - '10'
-script: yarn build
+script:
+  - yarn lint
+  - yarn build
 deploy:
   - provider: npm
     email: $NPM_EMAIL

package.json

@@ -54,7 +54,8 @@
     "build:es": "rollup --config rollup.config.js --format es --file dist/vue-mapbox-gl.esm.js --environment BUILD:prod,FORMAT:es",
     "build:unpkg": "rollup --config rollup.config.js --format iife --file dist/vue-mapbox-gl.min.js --environment BUILD:prod,FORMAT:iife",
     "build:demo": "rollup --config rollup.config.js --format iife --file dist/demo.min.js --environment BUILD:demo,FORMAT:iife",
-    "serve": "rimraf dist & rollup --config rollup.config.js --format iife --file dist/demo.min.js --environment BUILD:dev,FORMAT:iife --watch"
+    "serve": "rimraf dist & rollup --config rollup.config.js --format iife --file dist/demo.min.js --environment BUILD:dev,FORMAT:iife --watch",
+    "lint": "./node_modules/.bin/eslint src/**/*.{vue,ts}"
   },
   "dependencies": {
     "@mapbox/mapbox-gl-draw": "^1.1.2",