.travis.yml in closure_tree-6.6.0 vs .travis.yml in closure_tree-7.0.0

@@ -1,17 +1,17 @@
 cache: bundler
 sudo: false
 language: ruby
 rvm:
-  - 2.4.0
-  - 2.3.3
-  - 2.2.7
-# these haven't been passing for a while:
-#  - jruby-head
-#  - rbx
+  - 2.6.0
+  - 2.5.1
+  - 2.4.4
+  - 2.3.6
+  - 2.2.10
 
 gemfile:
+  - gemfiles/activerecord_5.2.gemfile
   - gemfiles/activerecord_5.1.gemfile
   - gemfiles/activerecord_5.0.gemfile
   - gemfiles/activerecord_4.2.gemfile
   - gemfiles/activerecord_edge.gemfile
 
@@ -25,5 +25,6 @@
 matrix:
   allow_failures:
     - gemfile: gemfiles/activerecord_edge.gemfile
     - rvm: jruby-head
     - rvm: rbx
+    - rvm: 2.6.0