Make sure icons are 30 x 30

[gmarty]

Though that wouldn't make any visual difference, icons with higher resolution (some are 1024 x 1024) are very likely to be more lightweigth when resize to 30 x 30.
That's because svgo can round decimal values so decreasing the resolution of an order of magnitude will also allow decimal values in paths to be a digit shorter.

That's very low priority though...