Ruby 2 / pdftk2

A few small changes for ruby 2 support, require pdftk-server version 2 which comes with UTF8 support, and bump the version to 1.1.0
Yes, I confirmed that running the tests with ruby 1.8.7 and this PR failed (bad me!), but after updating to your regex fix all the tests pass again.  So your fix works.

I also tested out a different fix at https://github.com/asee/pdf-toolkit/blob/master/lib/pdf/toolkit.rb#L319 that does the same thing that `ends_with?` was doing.  I think I have a preference for the regex version since I'm not sure if the string length and substring matching would be the same in all character sets.