Migrate to new Direct Messages endpoint

[avichalp]

Getting DMs throws an exception:

(direct-messages :oauth-creds my-creds :params {:count 50})

;; Twitter responded to request with error 34: Sorry, that page does
;; not exist.

I think it is because Twitter has changed the endpoints:

On September 17th, 2018 we retired the legacy Direct Message endpoints. If you had been using those endpoints, please make sure to migrate over to the new Direct Message endpoints or the Account Activity API.

The new endpoints are here in the migration guide.