CI: Use Ruby 2.4.7, 2.5.6, 2.6.4

Author: olleolleolle

.travis.yml

@@ -7,8 +7,8 @@ matrix:
   fast_finish: true
   include:
     # Latest versions first
-    - name: MRI 2.6.2 Latest
-      rvm: 2.6.2
+    - name: MRI 2.6.4 Latest
+      rvm: 2.6.4
     - name: JRuby 9.2.8.0 Latest on Java 11
       rvm: jruby-9.2.8.0
       jdk: oraclejdk11
@@ -18,16 +18,16 @@ matrix:
     - name: TruffleRuby Latest
       rvm: truffleruby
     - name: YARD uptodate in docs
-      rvm: 2.6.2
+      rvm: 2.6.4
       script:
       - bundle install --with documentation
       - bundle exec rake yard:master:uptodate
 
     # Older versions follow
-    - name: MRI 2.5.5
-      rvm: 2.5.5
-    - name: MRI 2.4.6
-      rvm: 2.4.6
+    - name: MRI 2.5.6
+      rvm: 2.5.6
+    - name: MRI 2.4.7
+      rvm: 2.4.7
     - name: MRI 2.3.8
       rvm: 2.3.8
     - name: MRI 2.2.10