[web] Attempt to fix long-right-angle-arrow

Summary: Attempted to fix the long-right-angle-arrow SVG to avoid the weird artifacts that were showing up in Safari.

Test Plan:
This seemed to work for me, would be good for @benschac to patch this and take another look.

Reviewers: def-au1t, palys-swm, benschac

Reviewed By: palys-swm, benschac

Subscribers: ashoat, Adrian, karol-bisztyga, yayabosh, benschac

Differential Revision: https://phabricator.ashoat.com/D3843