time: use secondsPerMinute instead of 60
time: use secondsPerMinute instead of 60

It's maybe better.

Change-Id: I7929e93a95c96676915bc24f2f7cce4e73b08c59
GitHub-Last-Rev: a8c2bb6cafe78090f35c3b194e270e301255be89
GitHub-Pull-Request: golang/go#26685
Reviewed-on: https://go-review.googlesource.com/126623
Reviewed-by: Ralph Corderoy <d6424ecc823ca663bdcbaea8e2d9df58a4d0e2b8@inputplus.co.uk>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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