Add prettier script and CI stage

Author: abraham

.prettierrc.json

@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}

.travis.yml

@@ -12,6 +12,8 @@ jobs:
       script: npm run build
     - name: Lint
       script: npm run lint
+    - name: Prettier
+      script: npm run prettier
     - name: Security
       script: npm audit && npm audit --prefix functions
     - stage: Test

package-lock.json

@@ -12,6 +12,8 @@
     "install:functions": "npm --prefix ./functions install",
     "lint": "eslint src",
     "postinstall": "npm run install:functions && npm run install:emulator",
+    "prettier:fix": "prettier . --write",
+    "prettier": "prettier . --check",
     "serve": "npm run build && firebase serve",
     "start": "cross-env NODE_ENV=development es-dev-server",
     "test:rules": "firebase emulators:exec --only firestore 'npx jest __tests__/*.rules.test.js'",
@@ -67,6 +69,7 @@
     "firebase-tools": "^7.15.1",
     "jest": "^25.1.0",
     "nunjucks": "^3.2.1",
+    "prettier": "2.0.1",
     "rimraf": "^3.0.2",
     "rollup": "^1.32.1",
     "rollup-plugin-copy": "^3.3.0",