Update node-sass for node v0.12 support

[calzoneman]

Hello,

Depending on node-sass@^1.2.3 causes issues with node v0.12 (and probably io.js as well); you can't install express-minify because the installation script for node-sass fails. If I clone express-minify locally and change the dependency in package.json to ^2.0.1 then everything installs correctly. The error has to do with the fact that node-sass has a C++ binding that needs to be rebuilt correctly for v0.12.

I can't speak for whether that causes breaking changes (my application doesn't use sass, and I don't see a changelog in the node-sass repo), but it'd be nice if express-minify could have that dependency updated so I don't have to fork it just to get it working on v0.12.

[calzoneman]

Possibly related to #19, but I don't have a Windows machine with node around to confirm.