Exclude Ruby 2.4.2 and Rails master from matrix

Author: krzysiek1507

.travis.yml

@@ -48,6 +48,7 @@ matrix:
   - { rvm: 2.1.10,        env: RAILS_VERSION=master }
   - { rvm: 2.2.8,        env: RAILS_VERSION=master }
   - { rvm: 2.3.5,        env: RAILS_VERSION=master }
+  - { rvm: 2.4.2,        env: RAILS_VERSION=master }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.0 }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.1 }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.2 }