comment: change slice to string in function comment/help

Comment is outdated, it should say a string is returned

Change-Id: I7d40135aac22845dbc1f91e02e5776cc7d58eda7
GitHub-Last-Rev: 08ee556
GitHub-Pull-Request: #75980
Reviewed-on: https://go-review.googlesource.com/c/go/+/713040
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Keith Randall <khr@google.com>

Author: redteampanda-ng

src/strings/strings.go

@@ -1085,8 +1085,9 @@ func trimRightUnicode(s, cutset string) string {
 	return s
 }
 
-// TrimSpace returns a slice of the string s, with all leading
-// and trailing white space removed, as defined by Unicode.
+// TrimSpace returns a slice (substring) of the string s,
+// with all leading and trailing white space removed,
+// as defined by Unicode.
 func TrimSpace(s string) string {
 	// Fast path for ASCII: look for the first ASCII non-space byte.
 	for lo, c := range []byte(s) {