remove debug output

[vicvega]

Just remove a line of output, causing an annoying dt to be printed repeatedly when running test.
See

$ rspec
[Coveralls] Set up the SimpleCov formatter.
[Coveralls] Using SimpleCov's default settings.
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Randomized with seed 43245
............................dt
dt
.dt
dt
...........................

[...]