Use conventional output for diffs in logfilter_test.go
Use conventional output for diffs in logfilter_test.go

Conventionally, "-got +want" is used for diffs in tests, rather than
"+got -want".

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