simplify logger time and avoid possible crashes (#13986)

time.Format() is not necessary prematurely for JSON
marshalling, since JSON marshalling indeed defaults
to RFC3339Nano.

This also ensures the 'time' is remembered until its
logged and it is the same time when the 'caller'
invoked 'log' functions.

internal/logger/logger.go

@@ -349,7 +349,7 @@ func logIf(ctx context.Context, err error, errKind ...interface{}) {
 		Host:         req.Host,
 		RequestID:    req.RequestID,
 		UserAgent:    req.UserAgent,
-		Time:         time.Now().UTC().Format(time.RFC3339Nano),
+		Time:         time.Now().UTC(),
 		API: &log.API{
 			Name: API,
 			Args: &log.Args{