Fix Gem Mine footprint

Fixes the gem mine's footprint.

1st pic - how it appears in editor
2nd pic - before patch
3rd pic - after patch
![footprints](https://cloud.githubusercontent.com/assets/566742/2623281/cb6e9b30-bce4-11e3-81e7-0a2f16aeabec.png)

Also looks like trees might not be right either.