Update to 2.3.6 on euwe. 😅

We previously tried to upgrade to 2.3.6 on euwe by backporting:
#15993

This was causing a hang in the automation test suite on euwe and we
reverted it in:
#16087

We now need to figure out why it's hanging so we can upgrade to 2.3.6+
on euwe.

.travis.yml

@@ -1,6 +1,6 @@
 language: ruby
 rvm:
-- '2.3.1'
+- '2.3.6'
 sudo: false
 cache:
   bundler: true