os: use Println instead of Printf in example
os: use Println instead of Printf in example

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It should use Println for consistency with other examples.

Change-Id: I49bd1652f9449fcbdd79c6b689c123090972aab3
Reviewed-on: https://go-review.googlesource.com/127836
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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