Make the active icon white

[bpierre]

This is a change of the active icon color to use white, for two reasons:

• To match the active state of the other Cinnamon tray icons.
• The red color is easy to mistake with an error state.

Note: I also optimized both icons through SVGO, let me know if you prefer not to.

[nicoulaj]

Indeed, I was afraid grey and white are not so easy to distinguish, but let's go ahead