change print to << to match pretty

[jamesepatrick]

I created issue #29 to explain this. In short the readme.md file says

By default the printers log to stdout but this can be changed by passing an object that responds to << message

Also the pretty printer also uses the << message instead of print.

[coveralls]

Coverage increased (+2.3%) to 93.973% when pulling 838e496 on jamesepatrick:master into 7ae382c on piotrmurach:master.

[coveralls]

Coverage remained the same at 91.721% when pulling 838e496 on jamesepatrick:master into 7ae382c on piotrmurach:master.

[piotrmurach]

Thanks ❤️