fix(hashmap2): Update incorrect assertion (rust-lang#660)

The test description says "at least five types of fruit", but the test itself is checking for exactly five types of fruit, which was a bit misleading for newcomers like me :) 

A simple change from "==" to ">=" should do the trick and successfully check for the "at least" condition.

exercises/collections/hashmap2.rs

@@ -68,7 +68,7 @@ mod tests {
         let mut basket = get_fruit_basket();
         fruit_basket(&mut basket);
         let count_fruit_kinds = basket.len();
-        assert!(count_fruit_kinds == 5);
+        assert!(count_fruit_kinds >= 5);
     }
 
     #[test]