Bump redis-store to 1.6.0

This version supports SSL/TLS via the redis:// URL scheme:
https://github.com/redis-store/redis-store/blob/master/CHANGELOG.md

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/47702

Gemfile.lock

@@ -676,7 +676,7 @@ GEM
       redis-actionpack (>= 5.0, < 6)
       redis-activesupport (>= 5.0, < 6)
       redis-store (>= 1.2, < 2)
-    redis-store (1.4.1)
+    redis-store (1.6.0)
       redis (>= 2.2, < 5)
     regexp_parser (0.5.0)
     representable (3.0.4)

Gemfile.rails5.lock

@@ -685,7 +685,7 @@ GEM
       redis-actionpack (>= 5.0, < 6)
       redis-activesupport (>= 5.0, < 6)
       redis-store (>= 1.2, < 2)
-    redis-store (1.4.1)
+    redis-store (1.6.0)
       redis (>= 2.2, < 5)
     regexp_parser (0.5.0)
     representable (3.0.4)