fix panic

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

vault.go

@@ -80,9 +80,10 @@ func (c *vaultConfig) Init(opts ...config.Option) error {
 		})
 		if err != nil && !c.opts.AllowFail {
 			return err
-		}
+		} else if err == nil {
 			token = rsp.Auth.ClientToken
 		}
+	}
 	cli.SetToken(token)
 
 	c.cli = cli