Update Redis client used for bucket notifications (#7213)

Current Redis client used https://github.com/garyburd/redigo/
has been archived and further development is done at
https://github.com/gomodule/redigo

This commit updates the client library accordingly.

Fixes #6392

vendor/github.com/gomodule/redigo/redis/go18.go

@@ -0,0 +1,9 @@
+// +build go1.8
+
+package redis
+
+import "crypto/tls"
+
+func cloneTLSConfig(cfg *tls.Config) *tls.Config {
+	return cfg.Clone()
+}