fix for docs&tests

docs/sanic/class_based_views.md

@@ -48,6 +48,24 @@ app.add_route(SimpleView.as_view(), '/')
 
 ```
 
+You can also use `async` syntax.
+
+```python
+from sanic import Sanic
+from sanic.views import HTTPMethodView
+from sanic.response import text
+
+app = Sanic('some_name')
+
+class SimpleAsyncView(HTTPMethodView):
+
+  async def get(self, request):
+      return text('I am async get method')
+
+app.add_route(SimpleAsyncView.as_view(), '/')
+
+```
+
 ## URL parameters
 
 If you need any URL parameters, as discussed in the routing guide, include them
@@ -128,4 +146,4 @@ view.add(['POST', 'PUT'], lambda request: text('I am a post/put method'))
 app.add_route(view, '/')
 ```
 
-Note: currently you cannot build a URL for a CompositionView using `url_for`. 
+Note: currently you cannot build a URL for a CompositionView using `url_for`.