Remove trailing whitespaces

src/libstd/future.rs

@@ -16,7 +16,7 @@
  *
  * ~~~
  * # fn fib(n: uint) -> uint {42};
- * # fn make_a_sandwich() {};  
+ * # fn make_a_sandwich() {};
  * let mut delayed_fib = std::future::spawn (|| fib(5000) );
  * make_a_sandwich();
  * println(fmt!("fib(5000) = %?", delayed_fib.get()))