bringing dependencies up to date

- dust-compiler-0.3.0 -> 0.3.1
- wrench-1.5.1 -> 1.5.4
- chai-1.7.2 -> 1.8.1
- grunt-contrib-jshint-0.6.3 -> 0.6.4
- grunt-mocha-test-0.6.3 -> 0.7.0
- mocha-1.12.0 -> 1.13.0

fixes #20 
fixes #21