.travis.yml in imap-backup-2.0.0 vs .travis.yml in imap-backup-2.1.0

@@ -1,9 +1,10 @@
 language: ruby
 rvm:
   - 2.3
   - 2.4
   - 2.5
+  - 2.6
 branches:
   only:
     - master
 before_install:
   - gem update --system