Exclude CI against Rails main branch for all ruby versions

Since Active Record Oracle enhanced adapter has not support Rails main branch yet.

Author: yahonda

.travis.yml

@@ -55,6 +55,20 @@ gemfile:
 
 matrix:
     exclude:
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 3.1.1
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 3.0.3
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 2.7.5
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 2.6.9
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 2.5.9
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 2.4.10
+       - gemfile: gemfiles/Gemfile.activerecord-main
+         rvm: 2.3.8
        - gemfile: gemfiles/Gemfile.activerecord-main
          rvm: jruby-head
        - gemfile: gemfiles/Gemfile.activerecord-main