Fix packetfu gem build warnings

[claudijd]

In the interest in getting us ready to build/release a new gem, I have tuned up the .gemspec so that it will build without semantic version warnings.

[claudijd]

@todb I was thinking we should consider a new PacketFu gem release since the last release was back in January 2014 and we've made a decent amount of changes since then. As part the prep for that idea, I tuned up the gemspec so it would stop throwing warnings.

[todb-r7]

Works for me!

todb@mazikeen:~/git/packetfu$ gem build packetfu.gemspec 
  Successfully built RubyGem
  Name: packetfu
  Version: 1.1.11
  File: packetfu-1.1.11.gem
[ruby-2.1.6@packetfu](master) 

I expect we'll release a version bump today. :)