doc: update next town hall date
![DataHub](docs/imgs/datahub-logo.png)
-> :mega: Next DataHub town hall meeting on April 3rd, 9am-10am PDT:
+> :mega: Next DataHub town hall meeting on April 17th, 9am-10am PDT:
> - [Signup sheet & questions](https://docs.google.com/spreadsheets/d/1hCTFQZnhYHAPa-DeIfyye4MlwmrY7GF4hBds5pTZJYM)
> - Details and recordings of past meetings can be found [here](docs/townhalls.md)
