go/jsonclient: increase test leeway
go/jsonclient: increase test leeway

Have observed failures with actual time being ~1.2 rather than
2.0 for the RFC1123 test, so increase leeway to 1 second.

google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go