Fix grammar in WebSocketContext::from_partially_read docs (#534)

Author: ZenPZero

src/protocol/mod.rs

@@ -387,7 +387,7 @@ impl WebSocketContext {
         Self::_new(role, FrameCodec::new(conf.read_buffer_size), conf)
     }
 
-    /// Create a WebSocket context that manages an post-handshake stream.
+    /// Create a WebSocket context that manages a post-handshake stream.
     ///
     /// # Panics
     /// Panics if config is invalid e.g. `max_write_buffer_size <= write_buffer_size`.