Test modern versions of Ruby

Author: bookernath

.travis.yml

@@ -1,11 +1,11 @@
 language: ruby
 rvm:
   - ruby-head
-  - 2.0
-  - 2.1
-  - 2.2
-  - 2.3
-  - 2.4
+  - 2.6
+  - 2.7
+  - 2.8
+  - 2.9
+  - 3.0
 cache:
   bundler: true
 sudo: false