strconv: add example for IsGraphic
strconv: add example for IsGraphic

Change-Id: I58ba1f5d5c942d6a345c19df1bca80b63fb5abf5
Reviewed-on: https://go-review.googlesource.com/132777
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

akutz/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,josharian/go,CAFxX/go,nawawi/go,akutz/go,nawawi/go,nawawi/go,CAFxX/go,akutz/go,nawawi/go,cloudflare/go,akutz/go,CAFxX/go,nawawi/go,akutz/go,josharian/go,cloudflare/go,CAFxX/go,cloudflare/go,cloudflare/go,josharian/go,golang/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,golang/go,cloudflare/go,akutz/go,golang/go,cloudflare/go,josharian/go,golang/go,josharian/go,akutz/go,golang/go,josharian/go,CAFxX/go,josharian/go,golang/go,josharian/go