[all] rake install task should use sudo on JRuby
[all] rake install task should use sudo on JRuby

* *NIX platforms only.
* SUDOLESS env may be set to prevent this behavior, but this brings it
  closer inline to how rake install works for MRI.

Signed-off-by: Alex Coles <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@alexcolesportfolio.com>

datamapper/dm-is-remixable