DEV: Run with Ruby 2.6.3 on Travis.

DEV: Run with Ruby 2.6.3 on Travis.

diff --git a/.travis.yml b/.travis.yml
index 7453fe8..39e59f6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -34,7 +34,7 @@ matrix:
   fast_finish: true
 
 rvm:
-  - 2.6.2
+  - 2.6.3
 
 services:
   - redis-server

GitHub sha: a7b840c2