doc: reduce overlong sentence

Author: tshepang

src/libstd/collections/hashmap.rs

@@ -675,7 +675,7 @@ impl DefaultResizePolicy {
 /// Hood bucket stealing.
 ///
 /// The hashes are all keyed by the task-local random number generator
-/// on creation by default, this means the ordering of the keys is
+/// on creation by default. This means that the ordering of the keys is
 /// randomized, but makes the tables more resistant to
 /// denial-of-service attacks (Hash DoS). This behaviour can be
 /// overridden with one of the constructors.