Add Explicit Chalk Dependency & Build Script

[Alec2435]

This PR does two things

1. Adds an explicit dependency on Chalk as otherwise certain package managers would incorrectly link the wrong version and as a result, Floggy wouldn't work
2. Add the build script to a "prepare" script to allow installing this package directly from Github. This is because otherwise Yarn/NPM don't know what to run to build the package when installing directly from the repo.

[habovh]

Approving this PR. The lack of having explicitly set chalk as a dependency or a peer dependency results in chalk being pruned when pruning dev dependencies. This leads to broken apps on Heroku for examples, or having to resort to keep all dev dependencies.

[jasonkuhrt]

Sorry @Alec2435 I missed this PR somehow. I've just fixed this though and will be cutting a new release soon fwiw. Thanks for the effort you put in here!