Banners: quick scaling fix for Maps

- scale to cover, not fit
- the SVG is still being fuzzy scaled though. Perhaps should replace
  all SVGs with higher res PNGs for now.

Fixes #439
1 job for <span class="ref-name">wip/jimmac/banner-maps</span> in 15 minutes and 14 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #244232
build-gnome-software

00:15:14