Automatic Content-Type values only work for lower case extensions

[dan-tull]

I ran into an issue in elm-reactor where static images with the extension jpg were served with a Content-Type header of image/jpeg while those with a JPG extension get application/octet-stream (the default).

If I'm reading it right, a call to toLower on the extension around here would fix it (all the extensions in the lookup table are conveniently already in lowercase):

snap-core/src/Snap/Internal/Util/FileServe.hs

Line 667 in b5ca1f0

mbe = Map.lookup ext m

I'd have made this a pull request, but I haven't learned Haskell (though knowing elm now I can read more of it than before) and its build toolchain yet.

Thanks!