Update new member example to not be broken.

Took forever but better late than never.

examples/new_member.py

@@ -9,7 +9,10 @@ class MyClient(discord.Client):
 
     async def on_member_join(self, member):
         guild = member.guild
-        await guild.default_channel.send('Welcome {0.mention} to {1.name}!'.format(member, guild))
+        if guild.system_channel is not None:
+            to_send = 'Welcome {0.mention} to {1.name}!'.format(member, guild)
+            await guild.system_channel.send(to_send)
+
 
 client = MyClient()
 client.run('token')