add test-unit gem in review.gemspec; Ruby 2.2.0 has no Test::Unit in default
add test-unit gem in review.gemspec; Ruby 2.2.0 has no Test::Unit in default

masawada/review,murashitas/review,krororo/review,takahashim/review,takahashim/review,kuad9/review_study,orangain/review,suzuki/review,suzuki/review,masawada/review,kmuto/review,kuad9/review_study,kmuto/review,krororo/review,murashitas/review,krororo/review,orangain/review,kmuto/review