io/fs: fix typo in comment

Change-Id: Idf8e5d808c0996e0ca00979e7b8d7627f29cd10f
Reviewed-on: https://go-review.googlesource.com/c/go/+/280552
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>

Author: douglarek

src/io/fs/walk.go

@@ -15,7 +15,7 @@ import (
 var SkipDir = errors.New("skip this directory")
 
 // WalkDirFunc is the type of the function called by WalkDir to visit
-// each each file or directory.
+// each file or directory.
 //
 // The path argument contains the argument to Walk as a prefix.
 // That is, if Walk is called with root argument "dir" and finds a file