added sloc v0.1.5

I packed the node cli app sloc [sloc](https://github.com/flosse/sloc) with npm2nix and `nodePackages.buildNodePackage`.  However there is an alternative way to do, e.g. like @matejc [tried it](https://gist.github.com/matejc/54a793979455c265baaa). Which way do you recommend for the future?