spec/pry_output_spec.rb: test colour leaks for Object literals

This ensures that CodeRay does not leak colours.
For more information see the following commit:

c544c1d69974e3505175d25fab69bb9e74674965
lib/pry.rb: keep randomness predictable!

Still a horrible hack, but at least it fixes issue
https://github.com/pry/pry/issues/988 (In PRY, srand() and rand()
results differs from IRB's or command line Ruby's).

I also would like to mention that the `result` variable also contains
some extra "\e[0m" sequences; it also messes Pry Theme up (singleton
objects) a bit.