test suite is broken on travis

[whyscream]

$ ruby test/test.rb
/home/travis/.rvm/rubies/ruby-2.2.7/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- minitest/autorun (LoadError)
	from /home/travis/.rvm/rubies/ruby-2.2.7/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:59:in `require'
	from test/test.rb:2:in `<main>'

The command "ruby test/test.rb" exited with 1.

Done. Your build exited with 1