Fix compilation error

file-info/make-http-format is now private:

> Exception in thread "main" java.lang.IllegalStateException: var: #'ring.middleware.file-info/make-http-format is not public, compiling:(clj_webjars.clj:41:12)

Not sure accessing private vars is the best way to go, but fixes things for now.
Merge pull request #1 from emlyn/patch-1

Fix compilation error