Update Reverse comment

Change-Id: I6e435391fc5d1d67af96ea88dcce3ccdd204d146

stringutil/reverse.go

@@ -17,7 +17,7 @@ limitations under the License.
 // Package stringutil contains utility functions for working with strings.
 package stringutil
 
-// Reverse returns the provided string with its runes in reverse order.
+// Reverse returns its argument string reversed rune-wise left to right.
 func Reverse(s string) string {
 	r := []rune(s)
 	for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {