remove 2.3.8, use rails 5.2 template

Author: DmytroStepaniuk

.travis.yml

@@ -4,7 +4,6 @@ sudo: false
 cache: bundler
 
 rvm:
-  - 2.3.8
   - 2.4.5
   - 2.5.5
   - 2.6.2
@@ -13,11 +12,11 @@ rvm:
 gemfile:
   - gemfiles/rails_5.0.gemfile
   - gemfiles/rails_5.1.gemfile
+  - gemfiles/rails_5.2.gemfile
 
 matrix:
   allow_failures:
     - rvm: ruby-head
-    - gemfile: gemfiles/rails_5.2.gemfile
 
 before_script:
   - psql -c 'drop database if exists api_session_recovering_app_test' -U postgres