Fixing deprecation warning in mongo-connect 0.5

Before:
```javascript
$ node app.js
connect-mongo deprecated auto_reconnect option is deprecated. Use autoReconnect instead app.js:82:10
Express server listening on port 3000 in development mode
```

After:
```javascript
$ node app.js
Express server listening on port 3000 in development mode
```

mongo-connect commit that made the change: https://github.com/kcbanner/connect-mongo/commit/663df675b6a5f9daaf937294abe2e4ba4ac7a1f2