Fix exclude matrix in travis config

Author: bricesanchez

.travis.yml

@@ -10,18 +10,12 @@ gemfile:
   - gemfiles/rails5.gemfile
 matrix:
   exclude:
-    - rvm: 2.3
+    - rvm: 2.6
       gemfile: gemfiles/rails3.gemfile
-    - rvm: 2.3
-      gemfile: gemfiles/rails4.gemfile
-    - rvm: 2.3
-      gemfile: gemfiles/rails5.gemfile
-    - rvm: 2.4
-      gemfile: gemfiles/rails5.gemfile
     - rvm: 2.5
-      gemfile: gemfiles/rails5.gemfile
-    - rvm: 2.6
-      gemfile: gemfiles/rails5.gemfile
+      gemfile: gemfiles/rails3.gemfile
+    - rvm: 2.4
+      gemfile: gemfiles/rails3.gemfile
 script: "bundle exec rake coverage"
 before_install:
   - gem install bundler