Updates jruby version in sinatra jruby fixture.
Updates jruby version in sinatra jruby fixture.

Co-authored-by: An Yu <446e9838deaeb979640d56c46523b7c882d598cd@pivotal.io>

cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack