Exclude js files ending in min.js from being processed by snockets

I had a problem with snockets reminifying `Rickshaw`. It would reminify an already minified rickshaw and the resulting code would not work. I don't see the value in reminifying js files that are already minified, so I patched connect-assets to ignore files ending in `min.js`.

Actually, the first thing I tried was to use script tags in express so that `connect-assets` wouldn't pick up these specific vendored assets, but it turns out that `connect-assets` only serves up files in its cache.