Update Tor Browser icon

[ingria]

The current icon is a bit outdated.

Icon name: torbrowser

Original icon	Numix icon

I know that tor-browser's icon is hardcoded, but some systems have an alternative package that does things properly.

• https://github.com/micahflee/torbrowser-launcher
• https://flathub.org/apps/details/com.github.micahflee.torbrowser-launcher