Update voxel-engine - fix position coords, new chunk gen

deathcap/voxel-engine@5efc028bfae1ffe155fd6d6beca7e4bce163f731 Update to g-s-fps-camera ^0.3.1, with position fix. Chunks now load consistently.

Commit message generated by https://github.com/deathcap/lmno-cl
Merge branch 'master' into gh-pages
Update demo: browserify demo.js > bundle.js