Some cleanup and travis updates

.travis.yml

@@ -1,17 +1,20 @@
 language: ruby
 
 rvm:
-  - 2.4.4
-  - 2.3.7
+  - 2.4.5
+  - 2.3.8
   - 2.2.10
 
 env:
+  - REDMINE_VER=4.0-stable DB=postgresql
   - REDMINE_VER=3.4-stable DB=postgresql
-  - REDMINE_VER=master DB=postgresql
 
 sudo: true
 cache: bundler
 
+addons:
+  postgresql: "9.6"
+
 notifications:
   webhooks:
     urls:
@@ -19,9 +22,6 @@ notifications:
     on_success: change
     on_failure: always
 
-addons:
-  postgresql: "9.6"
-
 before_install:
   - export PLUGIN_NAME=redmine_messenger
   - export REDMINE_GIT_REPO=git://github.com/redmine/redmine.git