Update 14-communicate-between-components.md for grammatical changes

Update to improve grammatical parallelism, as expressions separated by commas should share similar form.

BEFORE: Subscribe to events in `componentDidMount()`, unsubscribe in `componentWillUnmount()`, and when you receive an event, call `setState()`.
AFTER: Subscribe to events in `componentDidMount()`, unsubscribe in `componentWillUnmount()`, and call `setState()` when you receive an event.