Log Message:
openttd-data: Update to 0.6.0

OpenGFX 0.6.0 (29 Mar 2020)
---------------------------
- Add: NRT GUI sprites (#34)
- Change: Improved road tunnel construction GUI icons
- Change: hg -> git conversion
- Fix: realsprites animated flag for various features to suppress spurious \ 
warnings (#31)
- Fix: Sprite sizes and offsets were partially wrong (Brumi)
- Update translations: Dutch