[web] [fix] add cursor to button component
Summary: button component should have cursor. Unable to screenshot, but normal button behavior.
Test Plan: hand shows up on hover
Reviewers: atul, ashoat
Reviewed By: atul, ashoat
Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga
Differential Revision: https://phabricator.ashoat.com/D3137