Unbreak test/bench/task-perf-word-count-generic

Author: brson

src/test/bench/task-perf-word-count-generic.rs

@@ -20,7 +20,7 @@ use option::None;
 use std::map;
 use std::map::HashMap;
 use hash::Hash;
-use io::WriterUtil;
+use io::{ReaderUtil, WriterUtil};
 
 use std::time;