New backoff (#1153)

* new backoff function

* use backoff from util/backoff

* remove reset atemts

* change comment

* fmt

client/backoff.go

@@ -2,13 +2,13 @@ package client
 
 import (
 	"context"
-	"math"
 	"time"
+
+	"github.com/micro/go-micro/v2/util/backoff"
 )
 
 type BackoffFunc func(ctx context.Context, req Request, attempts int) (time.Duration, error)
 
-// exponential backoff is a function x^e multiplied by a factor of 0.1 second.
 func exponentialBackoff(ctx context.Context, req Request, attempts int) (time.Duration, error) {
-	return time.Duration(math.Pow(float64(attempts), math.E)) * time.Millisecond * 100, nil
+	return backoff.Do(attempts), nil
 }