Fix the test that fails on Rubinius

[kyrylo]

This is dependant on rubinius/rubinius#2940.

rubinius 2.2.5 (2.1.0 e543ba32 2014-02-08 JI) [x86_64-linux-gnu]

bacon -Itest -rubygems -a -q
Testing pry-stack_explorer version 0.4.9.1...
Ruby version: 2.1.0
...........................................F......................
Bacon::Error: [3, 3, 3, 3].==([0, 1, 2, 3]) failed
        /home/kyrylo/Dropbox/code/pry-stack_explorer/test/test_frame_manager.rb:60:in `__script__': FrameManager is Enumerable - should perform an Enumerable#map on the frames
        kernel/common/eval.rb:43:in `instance_eval'
        /home/kyrylo/Dropbox/code/pry-stack_explorer/test/test_frame_manager.rb:59:in `__script__'
        kernel/common/eval.rb:43:in `instance_eval'
        /home/kyrylo/Dropbox/code/pry-stack_explorer/test/test_frame_manager.rb:58:in `__script__'
        kernel/common/eval.rb:43:in `instance_eval'
        /home/kyrylo/Dropbox/code/pry-stack_explorer/test/test_frame_manager.rb:5:in `__script__'
        kernel/common/kernel.rb:447:in `load'
        kernel/bootstrap/array.rb:66:in `each'
        kernel/common/kernel.rb:447:in `load'
        kernel/delta/code_loader.rb:66:in `load_script'
        kernel/delta/code_loader.rb:152:in `load_script'
        kernel/loader.rb:649:in `script'
        kernel/loader.rb:831:in `main'