hello! using `mongodb@4.0.0-beta.6`

i'm trying to leverage session-level transactions following these instructions from the docs

the docs show an example with `session.getDatabase`, but typescript complains that the function signature `getDatabase` is missing from `ClientSession`

not sure if the function is available at runtime or not, but it's not in `mongodb.d.ts`

thought you folks should know

please advise if my usage is incorrect, thanks

  // chase