Update coffee-script to 1.8.0

coffee-script is at 1.8.0 now. Updating jest's dependency version should fix warnings that look like `npm WARN unmet dependency node_modules/jest-cli requires coffee-script@'1.7.1' but will load` when it is used in a package that depends oncoffee-script 1.8.0.

Here is the CS 1.8.0 change log: http://coffeescript.org/#changelog

Tested by running `npm test` and `cd examples/coffeescript; npm test`.