removing incompatible ruby-rails versions from travis

Author: gaorlov

.travis.yml

@@ -27,6 +27,24 @@ matrix:
       gemfile: gemfiles/4.1.gemfile
     - rvm: 2.4.1
       gemfile: gemfiles/4.2.gemfile
+    - rvm: 2.5.1
+      gemfile: gemfiles/4.0.gemfile
+    - rvm: 2.5.1
+      gemfile: gemfiles/4.1.gemfile
+    - rvm: 2.5.1
+      gemfile: gemfiles/4.2.gemfile
+    - rvm: 2.6.0
+      gemfile: gemfiles/4.0.gemfile
+    - rvm: 2.6.0
+      gemfile: gemfiles/4.1.gemfile
+    - rvm: 2.6.0
+      gemfile: gemfiles/4.2.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/4.0.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/4.1.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/4.2.gemfile
 # We need to install latest version of bundler, because one in travis
 # image is too old to recognize platform => :mri_22 in Gemfile.
 before_install: