Set a sensible viewBox

[tglman]

As today, the viewBox setting is commented out, I do not really know what that means and what could be a sensible value for it, so any help to figured it out is welcome, in any case things seems to work okish even without it.

here relevant code:

tileline/src/pieces.rs

Line 22 in 4f3e08f

// ("viewBox", &*format!("0 0 {} {}", width, height)),