use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/xenolf/lego/platform/wait/wait.go

@@ -0,0 +1,33 @@
+package wait // import "github.com/xenolf/lego/platform/wait"
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/xenolf/lego/log"
+)
+
+// For polls the given function 'f', once every 'interval', up to 'timeout'.
+func For(msg string, timeout, interval time.Duration, f func() (bool, error)) error {
+	log.Infof("Wait for %s [timeout: %s, interval: %s]", msg, timeout, interval)
+
+	var lastErr string
+	timeUp := time.After(timeout)
+	for {
+		select {
+		case <-timeUp:
+			return fmt.Errorf("time limit exceeded: last error: %s", lastErr)
+		default:
+		}
+
+		stop, err := f()
+		if stop {
+			return nil
+		}
+		if err != nil {
+			lastErr = err.Error()
+		}
+
+		time.Sleep(interval)
+	}
+}