time: fix incorrect "zero pad" comment in example
time: fix incorrect "zero pad" comment in example

The comment currently implies that a zero will be added, but the
underscore is used to add a space for single-digit dates.

Change-Id: Ib3bac8a16bc2d1fcb26ab3bb7ad172b89e1a4a24
Reviewed-on: https://go-review.googlesource.com/75230
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

nawawi/go,golang/go,Cofyc/go,nawawi/go,golang/go,akutz/go,CAFxX/go,josharian/go,CAFxX/go,golang/go,codestation/go,akutz/go,akutz/go,nawawi/go,golang/go,codestation/go,codestation/go,cloudflare/go,golang/go,CAFxX/go,golang/go,cloudflare/go,josharian/go,CAFxX/go,cloudflare/go,akutz/go,akutz/go,Cofyc/go,codestation/go,Cofyc/go,josharian/go,cloudflare/go,nawawi/go,codestation/go,codestation/go,josharian/go,golang/go,codestation/go,cloudflare/go,CAFxX/go,christopher-henderson/Go,akutz/go,codestation/go,josharian/go,josharian/go,Cofyc/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,josharian/go,akutz/go,nawawi/go,josharian/go,CAFxX/go,golang/go,Cofyc/go,CAFxX/go,Cofyc/go,akutz/go,Cofyc/go,nawawi/go,cloudflare/go,Cofyc/go,cloudflare/go