Merge pull request #38 from dunglas/watch

Add a watch script

Author: soyuka

package.json

@@ -43,7 +43,8 @@
     "lint": "eslint src && flow check",
     "fix": "eslint --fix src",
     "eslint-check": "eslint --print-config .eslintrc.js | eslint-config-prettier-check",
-    "build": "babel src -d lib --ignore '*.test.js'"
+    "build": "babel src -d lib --ignore '*.test.js'",
+    "watch": "babel src -d lib --ignore '*.test.js' --watch"
   },
   "jest": {
     "automock": false,