Update spec files to make them run with ruby 1.9.3p484, 2.0.0p457 and 2.1.2p95
and with rspec 3.0.0.
Update packetfu.gemspec: rspec must be >= 2.14.1.
Add rspec-its as development dependency in gemspec.
Merge pull request #66 from sdaubert/ruby21

Update spec files to make them run with rspec 3.0.0 and ruby >= 1.9.3