Fixes broken references on Ruby v1.9.x

[lee-dohm]

Calling to_s on an array containing strings results in different output on Ruby v1.8 and v1.9:

% rvm all do ruby -e 'puts ["foo", "bar", "baz"].to_s'
foobarbaz
["foo", "bar", "baz"]

But join works the same:

% rvm all do ruby -e 'puts ["foo", "bar", "baz"].join(" ")'
foo bar baz
foo bar baz

So I changed the to_s to join("\n").

[travisbot]

This pull request passes (merged 071bb40 into f91f733).