adds "build:watch" script

Author: bkrem

package.json

@@ -8,6 +8,7 @@
     "clean:lib": "rimraf lib/*",
     "precommit": "lint-staged",
     "build": "yarn clean:lib && webpack --progress --colors --env build",
+    "build:watch": "yarn clean:lib && webpack --progress --colors --watch --env build",
     "dev": "yarn clean:lib && webpack --progress --colors --watch --env dev",
     "lint": "eslint src/**/*.js",
     "test": "yarn lint && jest --coverage --verbose",