upgrade ruby/redmine version matrix in .travis.yml
upgrade ruby/redmine version matrix in .travis.yml

 - rvm: 2.2.6 → 2.2.7
 - rvm: 2.3.3 → 2.3.4
 - rvm: 2.4.1 (new)
 - REDMINE_VERSION=3.2.5 → 3.2.6
 - REDMINE_VERSION=3.3.2 → 3.3.3
cat-in-136/redmine_scheduling_poll,cat-in-136/redmine_scheduling_poll