run formatting check as part of ci

Author: bcherny

package.json

@@ -16,12 +16,13 @@
     "build:server": "tsc -d",
     "clean": "shx rm -rf dist && mkdir dist",
     "format": "prettier \"**/*.ts\" --write",
+    "format-check": "prettier \"**/*.ts\" --check",
     "lint": "eslint src/*.ts test/*.ts",
     "tdd": "concurrently -r -p '' -k 'npm run watch' 'npm run watch:test'",
     "test": "npm run pre-test && ava --timeout=300s --verbose",
     "stresstest": "seq 1 10 | xargs -I{} npm test",
     "prepublishOnly": "npm test",
-    "pre-test": "npm run clean && npm run build:server",
+    "pre-test": "npm run clean && npm run format-check && npm run build:server",
     "watch": "tsc -w",
     "watch:test": "ava -w"
   },