Run travis tests against ruby 2.3.1
Run travis tests against ruby 2.3.1

[#128688905]

Signed-off-by: Andrew Crump <bad96bc28586e95c5d7da81c13d926ea5028b22f@pivotal.io>

cloudfoundry/cf-mysql-broker,cloudfoundry/cf-mysql-broker,cloudfoundry/cf-mysql-broker