Explicitly require MimeType from ActionDispatch
Explicitly require MimeType from ActionDispatch

Fixes:   https://travis-ci.org/amatsuda/kaminari/jobs/45531644#L1127-L1239
Related: https://github.com/rails/rails/issues/17030

kaminari/kaminari-sinatra,kaminari/kaminari-sinatra,kaminari/kaminari-sinatra