NPM: Set chalk as a dependency, not a devDependency

Fixes #4

chalk is 100% needed to make this run.

For what I read, it's not a case to set it into the peerDependencies list, because it isn't optional. Although, I can be wrong as I'm not used on node modules.

Refs: npm/npm#1400 & http://blog.nodejs.org/2013/02/07/peer-dependencies/