Ensure CI fails on non-prettier compliant PRs (#693)

.prettierrc

@@ -4,6 +4,5 @@
   "useTabs": false,
   "semi": true,
   "tabWidth": 2,
-  "trailingComma":
-    "none"
+  "trailingComma": "none"
 }

.travis.yml

@@ -20,6 +20,8 @@ install:
 
 jobs:
   include:
+    - stage: test
+      script: npm run prettier:diff
     - stage: test
       script: npm run test
     - stage: test

package.json

@@ -141,7 +141,10 @@
     "tscheck": "tsc --noEmit",
     "start": "npm run dev",
     "precommit": "lint-staged",
-    "formatAll": "find ./common/ -name '*.ts*' | xargs prettier --write --config ./.prettierrc --config-precedence file-override",
+    "formatAll":
+      "find ./common/ -name '*.ts*' | xargs prettier --write --config ./.prettierrc --config-precedence file-override",
+    "prettier:diff":
+      "prettier --write --config ./.prettierrc --list-different \"common/**/*.ts\" \"common/**/*.tsx\"",
     "prepush": "npm run tslint && npm run tscheck"
   },
   "lint-staged": {