Update tested ruby versions in travis

Author: tom-lord

.travis.yml

@@ -1,12 +1,9 @@
 language: ruby
 rvm:
- - 2.0.0
- - 2.1.10
- - 2.2.10
- - 2.3.8
  - 2.4.5
  - 2.5.5
- - 2.6.2
+ - 2.6.2 # Uses unicode 12.0.0
+ - 2.6.3 # Uses unicode 12.1.0
  - ruby-head
 matrix:
  allow_failures: