remove cautionary wording in the hashmap docstring

it's pretty solid, at least relative to most of the other modules

Author: thestinger

src/libcore/hashmap.rs

@@ -8,11 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/*!
-
-Sendable hash maps.  Very much a work in progress.
-
-*/
+//! Sendable hash maps.
 
 // NB: transitionary, de-mode-ing.
 #[forbid(deprecated_mode)];