all: fix some comments

Change-Id: Id334943c9be6e035d52a8d8a4bd26e0e31ae9791
Reviewed-on: https://go-review.googlesource.com/c/tools/+/492578
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Tim King <taking@google.com>
Run-TryBot: shuang cui <imcusg@gmail.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
diff --git a/godoc/dirtrees.go b/godoc/dirtrees.go
index f6a5ba0..51aa1f3 100644
--- a/godoc/dirtrees.go
+++ b/godoc/dirtrees.go
@@ -220,7 +220,7 @@
 	// The root could be a symbolic link so use Stat not Lstat.
 	d, err := c.fs.Stat(root)
 	// If we fail here, report detailed error messages; otherwise
-	// is is hard to see why a directory tree was not built.
+	// is hard to see why a directory tree was not built.
 	switch {
 	case err != nil:
 		log.Printf("newDirectory(%s): %s", root, err)