Add percy script to Travis CI

Author: hacknug

.travis.yml

@@ -12,3 +12,4 @@ cache:
 script:
   - yarn install
   - yarn run build
+  - npx percy snapshot build/

package.json

@@ -46,6 +46,7 @@
     "eslint-plugin-standard": "^4.0.0",
     "npm-run-all": "^4.1.5",
     "parcel-plugin-bundle-visualiser": "^1.2.0",
+    "percy": "^0.9.0",
     "postcss-cli": "^6.1.3",
     "postcss-fontpath": "^1.0.0",
     "posthtml-expressions": "^1.1.1",