Merge branch 'zj-prometheus' into 'master'

...thub.com/prometheus/client_golang/prometheus/collector.go

...github.com/prometheus/client_golang/prometheus/counter.go

...or/github.com/prometheus/client_golang/prometheus/desc.go

vendor/github.com/prometheus/client_golang/prometheus/doc.go

...m/prometheus/client_golang/prometheus/expvar_collector.go

vendor/github.com/prometheus/client_golang/prometheus/fnv.go

...r/github.com/prometheus/client_golang/prometheus/gauge.go

...b.com/prometheus/client_golang/prometheus/go_collector.go

...thub.com/prometheus/client_golang/prometheus/histogram.go

...or/github.com/prometheus/client_golang/prometheus/http.go

.../github.com/prometheus/client_golang/prometheus/metric.go

.../prometheus/client_golang/prometheus/process_collector.go

....com/prometheus/client_golang/prometheus/promhttp/http.go

...ithub.com/prometheus/client_golang/prometheus/registry.go

...github.com/prometheus/client_golang/prometheus/summary.go

...github.com/prometheus/client_golang/prometheus/untyped.go

...r/github.com/prometheus/client_golang/prometheus/value.go

vendor/github.com/prometheus/client_golang/prometheus/vec.go

vendor/github.com/prometheus/client_model/AUTHORS.md

vendor/github.com/prometheus/client_model/LICENSE