Italian translation fixes

Change-Id: I1dec07f6a3e721a4f35c8cde2da136e34d8e4cb2
Reviewed-on: https://code.wireshark.org/review/4915
Reviewed-by: Evan Huus <eapache@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>