fix golint issues in core/utils (#520)

* fix golint issues in core/utils

* fix golint issues in core/trace

* fix golint issues in core/trace

core/utils/times.go

@@ -7,32 +7,39 @@ import (
 	"github.com/tal-tech/go-zero/core/timex"
 )
 
+// A ElapsedTimer is a timer to track the elapsed time.
 type ElapsedTimer struct {
 	start time.Duration
 }
 
+// NewElapsedTimer returns a ElapsedTimer.
 func NewElapsedTimer() *ElapsedTimer {
 	return &ElapsedTimer{
 		start: timex.Now(),
 	}
 }
 
+// Duration returns the elapsed time.
 func (et *ElapsedTimer) Duration() time.Duration {
 	return timex.Since(et.start)
 }
 
+// Elapsed returns the string representation of elapsed time.
 func (et *ElapsedTimer) Elapsed() string {
 	return timex.Since(et.start).String()
 }
 
+// ElapsedMs returns the elapsed time of string on milliseconds.
 func (et *ElapsedTimer) ElapsedMs() string {
 	return fmt.Sprintf("%.1fms", float32(timex.Since(et.start))/float32(time.Millisecond))
 }
 
+// CurrentMicros returns the current microseconds.
 func CurrentMicros() int64 {
 	return time.Now().UnixNano() / int64(time.Microsecond)
 }
 
+// CurrentMillis returns the current milliseconds.
 func CurrentMillis() int64 {
 	return time.Now().UnixNano() / int64(time.Millisecond)
 }