[Cashtab] Faster transition for opening and closing hamburger menu

Summary:
Now that we have a bigger menu and more items, the open time is a bit too dramatic.

Make it faster.

Test Plan: npm start and open/close the menu, confirm it is faster

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16003