fmt: remove unnecessary trailing commas in doc.go

Change-Id: Ib5efe172c55ff624b6771c2f02c466e35ba6cc50
Reviewed-on: https://go-review.googlesource.com/45090Reviewed-by: Rob Pike <r@golang.org>

src/fmt/doc.go

@@ -192,9 +192,9 @@
 	For example,
 		fmt.Sprintf("%[2]d %[1]d\n", 11, 22)
 	will yield "22 11", while
-		fmt.Sprintf("%[3]*.[2]*[1]f", 12.0, 2, 6),
+		fmt.Sprintf("%[3]*.[2]*[1]f", 12.0, 2, 6)
 	equivalent to
-		fmt.Sprintf("%6.2f", 12.0),
+		fmt.Sprintf("%6.2f", 12.0)
 	will yield " 12.00". Because an explicit index affects subsequent verbs,
 	this notation can be used to print the same values multiple times
 	by resetting the index for the first argument to be repeated: