Fix std::fs::read_dir test expectations

The std::fs::read_dir test has the wrong expectations after a new
fixture was added to the fixtures directory.

This corrects that.

src/bin/std_fs_read_dir.rs

@@ -6,7 +6,7 @@
 
 fn main() {
   let entries = std::fs::read_dir("fixtures").unwrap();
-  assert_eq!(entries.count(), 4);
+  assert_eq!(entries.count(), 5);
 
   let entries = std::fs::read_dir("fixtures/directory").unwrap();
   assert_eq!(entries.count(), 2);