Fix Sanic arg

I assume the value of `__name__` (module name) was intended.

docs/middleware.md

@@ -7,7 +7,7 @@ Middleware is registered via the middleware decorator, and can either be added a
 ## Examples
 
 ```python
-app = Sanic('__name__')
+app = Sanic(__name__)
 
 @app.middleware
 async def halt_request(request):
@@ -26,4 +26,4 @@ async def handler(request):
 	return text('I would like to speak now please')
 
 app.run(host="0.0.0.0", port=8000)
-```
+```