ios safari 弹出对话框时程序被阻塞

* **Macaca Version**:
2.0.13
* **Macaca Doctor Logs**:

macaca-doctor version: 2.0.5

Node.js checklist:

node env: /usr/local/bin/node
node version: v8.9.3

iOS checklist:

Xcode Command Line Tools is ready, version: 2349.
xcodebuild version: 9.2
iproxy[usbmuxd] is installed at: `/usr/local/bin/iproxy`
ios_webkit_debug_proxy is installed at: `/usr/local/bin/ios_webkit_debug_proxy`
carthage is installed, version: 0.29.0

Android checklist:

JAVA version is `1.8.0_101`
JAVA_HOME is set to `/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home`
ANDROID_HOME is set to `/Users/gaobester/Library/Android/sdk`
Platforms is set to `/Users/gaobester/Library/Android/sdk/platforms/android-27`
ADB tool is set to `/Users/gaobester/Library/Android/sdk/platform-tools/adb`
gradle is installed, version: 4.5

Installed driver list:

android: 2.0.46
ios: 2.0.30

* **Operate System**:
macos 10.13.4

* **Programming Language**:
Java

测试ios的safari浏览器。客户端使用的是java语言，调用macaca-java API。

当html中弹出alert弹窗后。java程序被阻塞，不能再往下执行。
只有在ios的safari上手动点击alert弹窗，弹窗消失后java程序才继续往下执行。

因此，当html有弹窗时，java程序就被阻塞住了。
请问如何解决这个问题？

Start by reproducing the reported alert flow through the Macaca Java API on iOS Safari, using the versions and environment listed in the issue. Read the API's handling of Safari alert dialogs and compare execution before and after the alert is manually dismissed; done means the Java program continues without manual interaction.

Written by the indexing model from the issue text.