Store your data in ProBot database easily, using the embed messages feature, for free :).
npm install probot.db
Now all you need is the server id that has ProBot in, and your auth token from probot.io.
const Database = require('probot.db');
const database = new Database('auth token', 'server id', { embedName: 'probot.db' });
await database.set('foo', 'bar');
await database.get('foo'); // bar
await database.delete('foo');
await database.clear();