strconv: use go generate to create isprint.go

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/132230043
diff --git a/src/pkg/strconv/isprint.go b/src/pkg/strconv/isprint.go
index ba0adbd..80738ed 100644
--- a/src/pkg/strconv/isprint.go
+++ b/src/pkg/strconv/isprint.go
@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // DO NOT EDIT.  GENERATED BY
-//     go run makeisprint.go >x && mv x isprint.go
+//     go run makeisprint.go -output isprint.go
 
 package strconv