Use `open <url>` on macOS instead of webbrowser module.

Review Request #8959 — Created May 23, 2017 and submitted — Latest diff uploaded

Information

RBTools
release-0.7.x
9e7edd0...

Reviewers

There's currently a bug in the interaction between AppleScript on the latest
macOS and python's webbrowser module which is causing URL opens to fail. This
change moves us over to using macOS's open command instead, which is likely
the way that Python is going to go.

Posted this change and opened it successfully.