Fix reference to frame module.

src/proto/value.rs

@@ -13,7 +13,7 @@
 //!   * Pairs are serialized as two consecutive values.
 //!   * Vectors are serialized as length-prefixed arrays of serialized values.
 //!
-//! See the `frame_codec` module for the codec applied to byte streams.
+//! See the `frame` module for the codec applied to byte streams.
 
 use std::io;
 use std::net;