Correct ClientException message raised in invocation hooks.

For when the hooks are not coroutines.

discord/ext/commands/bot.py

@@ -387,7 +387,7 @@ class BotBase(GroupMixin):
             The coroutine is not actually a coroutine.
         """
         if not asyncio.iscoroutinefunction(coro):
-            raise discord.ClientException('The error handler must be a coroutine.')
+            raise discord.ClientException('The pre-invoke hook must be a coroutine.')
 
         self._before_invoke = coro
         return coro
@@ -420,7 +420,7 @@ class BotBase(GroupMixin):
             The coroutine is not actually a coroutine.
         """
         if not asyncio.iscoroutinefunction(coro):
-            raise discord.ClientException('The error handler must be a coroutine.')
+            raise discord.ClientException('The post-invoke hook must be a coroutine.')
 
         self._after_invoke = coro
         return coro

discord/ext/commands/core.py

@@ -612,7 +612,7 @@ class Command:
             The coroutine is not actually a coroutine.
         """
         if not asyncio.iscoroutinefunction(coro):
-            raise discord.ClientException('The error handler must be a coroutine.')
+            raise discord.ClientException('The pre-invoke hook must be a coroutine.')
 
         self._before_invoke = coro
         return coro
@@ -639,7 +639,7 @@ class Command:
             The coroutine is not actually a coroutine.
         """
         if not asyncio.iscoroutinefunction(coro):
-            raise discord.ClientException('The error handler must be a coroutine.')
+            raise discord.ClientException('The post-invoke hook must be a coroutine.')
 
         self._after_invoke = coro
         return coro