Allow 'rediss' scheme to define whether SSL is enabled

If the URL uses the 'rediss' scheme, SSL should be enabled. This follows the
behaviour of Redix standalone and embedded in other libraries.

lib/phoenix_pubsub_redis/redis.ex

@@ -23,7 +23,7 @@ defmodule Phoenix.PubSub.Redis do
     * `:host` - The redis-server host IP, defaults `"127.0.0.1"`
     * `:port` - The redis-server port, defaults `6379`
     * `:password` - The redis-server password, defaults `""`
-    * `:ssl` - The redis-server ssl option, defaults `false`
+    * `:ssl` - The redis-server ssl option, defaults `false`, unless the URL scheme is `rediss`
     * `:redis_pool_size` - The size of the redis connection pool. Defaults `5`
     * `:compression_level` - Compression level applied to serialized terms - from `0` (no compression), to `9` (highest). Defaults `0`
     * `:socket_opts` - List of options that are passed to the network layer when connecting to the Redis server. Default `[]`
@@ -111,9 +111,12 @@ defmodule Phoenix.PubSub.Redis do
         [username, password] -> [username: username, password: password]
       end
 
+    ssl = info.scheme == "rediss"
+
     opts
     |> Keyword.merge(user_opts)
     |> Keyword.merge(host: info.host, port: info.port || @defaults[:port])
+    |> Keyword.put(:ssl, ssl)
   end
 
   defp validate_node_name!(node_name) do