Update redis-rb to 4.1.3 to match GitLab CE/EE.

One bug fix: https://github.com/redis/redis-rb/blob/master/CHANGELOG.md

Gemfile.lock

@@ -26,7 +26,7 @@ GEM
     rack-protection (2.0.7)
       rack
     rainbow (2.1.0)
-    redis (4.1.2)
+    redis (4.1.3)
     redis-namespace (1.6.0)
       redis (>= 3.0.4)
     rspec (3.7.0)