Revert "Require mime-type in development to fix build on 1.9.3"
Revert "Require mime-type in development to fix build on 1.9.3"

This reverts commit 31a3eb35b18406b8893e9659325557f5db16cc93.

jlberglund/mandrill_dm,spovich/mandrill_dm,envato/mandrill_dm