Fix typo round_robbin -> round_robin in emqx.schema

etc/emqx.conf

@@ -2122,7 +2122,7 @@ broker.session_locking_strategy = quorum
 ##
 ## Value: Enum
 ## - random
-## - round_robbin
+## - round_robin
 ## - sticky
 ## - hash
 broker.shared_subscription_strategy = random

priv/emqx.schema

@@ -1996,11 +1996,11 @@ end}.
 
 %% @doc Shared Subscription Dispatch Strategy.
 {mapping, "broker.shared_subscription_strategy", "emqx.shared_subscription_strategy", [
-  {default, round_robbin},
+  {default, round_robin},
   {datatype,
    {enum,
     [random, %% randomly pick a subscriber
-     round_robbin, %% round robin alive subscribers one message after another
+     round_robin, %% round robin alive subscribers one message after another
      sticky, %% pick a random subscriber and stick to it
      hash %% hash client ID to a group member
     ]}}
@@ -2125,4 +2125,4 @@ end}.
   [{check_interval, cuttlefish:conf_get("vm_mon.check_interval", Conf)},
    {process_high_watermark, cuttlefish:conf_get("vm_mon.process_high_watermark", Conf)},
    {process_low_watermark, cuttlefish:conf_get("vm_mon.process_low_watermark", Conf)}]
-end}.
+end}.