mark context as modified after writing data

src/context.rs

@@ -164,6 +164,7 @@ impl<A, S> HttpContext<A, S> where A: Actor<Context=Self> {
             self.stream = Some(SmallVec::new());
         }
         self.stream.as_mut().map(|s| s.push(frame));
+        self.inner.modify();
     }
 
     /// Handle of the running future