Add postdeploy script

Author: yefim

app.json

@@ -7,6 +7,9 @@
     "sample"
   ],
   "repository": "https://github.com/yefim/flask-heroku-sample",
+  "scripts": {
+    "postdeploy": "python -c 'from app import db; db.create_all()'"
+  },
   "addons": [
     "heroku-postgresql"
   ]