Fix encoding issues in specs for Ruby 2.x

I tried running PacketFu specs on Ruby 2.0.0-p353 and it failed due to some encoding expectation issues in the specs.  I fixed those up with forced encoding so we can get it passing across the board.

These specs now pass on:

- 1.9.3p484
- 2.0.0-p353
- 2.1.0

Yay!