Move pry to development dependency
Move pry to development dependency

Fixes https://github.com/travis-ci/travis.rb/issues/227

We'll revisit dropping 1.8.x support when we bump this
to version 1.8.

prabagithub/travis.rb,Tiger66639/travis.rb,chriskuehl/travis.rb,chriskuehl/travis.rb,Zearin/travis.rb,Tiger66639/travis.rb,snordhausen/travis.rb,deivid-rodriguez/travis.rb,doct15/travis.rb,vinaykaradia/rubyBuildClone,snordhausen/travis.rb,danishkhan/travis.rb,Zearin/travis.rb,doct15/travis.rb,whip112/travis.rb,prabagithub/travis.rb,travis-ci/travis.rb,deivid-rodriguez/travis.rb,whip112/travis.rb,travis-ci/travis.rb,vinaykaradia/rubyBuildClone,vinaykaradia/rubyBuildClone,whip112/travis.rb,travis-ci/travis.rb,prabagithub/travis.rb,deivid-rodriguez/travis.rb,doct15/travis.rb,Tiger66639/travis.rb,chriskuehl/travis.rb,danishkhan/travis.rb,snordhausen/travis.rb,danishkhan/travis.rb,Zearin/travis.rb