New messages are hidden under third party keyboards

[Reported by @cities7:matrix.org in #riot-ios using SwiftKey](https://matrix.to/#/!tDRGDwZwQnlkowsjsm:matrix.org/$1521251286139088EDHzS:matrix.org) (I can confirm it using Gboard)

When you are using a third party keyboard and you tap the send a message box to get ready to type in a message, the app hides all of the recent messages behind the keyboard. New messages that you send are also hidden behind the keyboard and you have to manually scroll down to see them.

When you tap on the send a message box with the standard keyboard, Riot automatically scrolls the messages so that they are visible and new messages remain visible as they are sent.