Drop support for 2.0.0 as it is no longer supported

eregon · eregon · commit 245862558761 · 2016-03-17T11:24:39.000+01:00
* See https://www.ruby-lang.org/en/news/2016/02/24/support-plan-of-ruby-2-0-0-and-2-1/
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,6 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.0.0-p648
   - 2.1.8
   - 2.2.4
   - ruby-head
