fixing #24 : test fails due a Bang!

[zeroed]

My humble commit would fix the #24 failures:

eddie@white:~/Coding/map$ ruby test/map_test.rb 
Loaded suite test/map_test
Started
.........................................................

Finished in 0.207305203 seconds.

57 tests, 4956 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
100% passed

274.96 tests/s, 23906.78 assertions/s

I hope this is the expected behaviour...
Yup!

^_^