.travis.yml in doit-0.3.6 vs .travis.yml in doit-0.3.9

@@ -3,10 +3,14 @@
 
 bundler_args: --without production
 script: "bundle exec rake test"
 
 rvm:
-  - 2.6.1
+  - 2.6.6  # 2020-07-17
+#  - 2.6.5  # 2019-10-29
+#  - 2.6.4  # 2019-10-15
+#  - 2.6.3  # 2019-06-21
+#  - 2.6.1
 #  - 2.5.1
 #  - 2.5.0
 #  - 2.4.1
 #  - 2.3.0  # tested; no longer in CI
 #  - 2.2.3  # tested; no longer in CI