Bump version to 4.19.0
Bump version to 4.19.0

Summary: Update version

Reviewers: bigly, arik

Reviewed By: arik

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D7714

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS