Update gray-matter to v4

[bjankord]

Seeing a npm warning about:

npm WARN deprecated [email protected]: CoffeeScript on NPM has moved to "coffeescript" (no hyphen)

Looks like gray-matter v4 updated to use coffeescript instead of coffee-script. Updating the gray-matter would resolve this npm deprecation warning. 👍

[JasonKleban]

This is a dependency in ts-loader that prevents npm link from working because of a systax error (on Windows at least?) Removing the dependency in ts-loader (which will break some npm scripts) will let npm link preinstall activities succeed.