Fix spec encoding problem under Ruby 2.0.0.

This fixes the spec failure under [Ruby 2.0.0p0](https://travis-ci.org/ddollar/foreman/jobs/5232121).

It doesn't look like you're maintaining 1.8.7 compatibility (at least the travis config makes it seem that way), but if you were, you'd probably want to split the `force_encoding` call onto a line by itself with a `respond_to?` guard.