Merge #647

647: Add optional message argument to ping r=badboy

According to Redis, you can pass an optional argument to PING. To be consistent with their API, I've added that optional argument

Author: not-a-robot[bot]

lib/redis.rb

@@ -143,10 +143,11 @@ def select(db)
 
   # Ping the server.
   #
+  # @param [optional, String] message
   # @return [String] `PONG`
-  def ping
+  def ping(message = nil)
     synchronize do |client|
-      client.call([:ping])
+      client.call([:ping, message].compact)
     end
   end