.travis.yml in ridgepole-0.7.5 vs .travis.yml in ridgepole-0.7.6

@@ -4,16 +4,13 @@
 language: ruby
 cache:
   - bundler
   - apt
 rvm:
-  - 2.3.6
+  - 2.3.8
   - 2.4.5
   - 2.5.3
-  - 2.6.0-preview2
-matrix:
-  allow_failures:
-    - rvm: 2.6.0-preview2
+  - 2.6.0
 before_script:
   - sudo service mysql stop
   - sudo service postgresql stop
   - for i in {1..60}; do docker-compose up -d && break; sleep 1; done
   - function mysql_ping { mysqladmin -u root -h 127.0.0.1 -P 13316 -ppassword ping; }