Cordova Android项目如何做代码混淆

我想修改build.gradle配置 可是这个文件明确写了
// GENERATED FILE! DO NOT EDIT!
可是还是试了试：

if (cdvReleaseSigningPropertiesFile) {

        signingConfigs {
            release {
                // These must be set or Gradle will complain (even if they are overridden).
                keyAlias = ""
                keyPassword = "__unset"
                // And these must be set to non-empty in order to have the signing step added to the task graph.
                storeFile = null
                storePassword = "__unset"
            }
        }
        buildTypes {
            release {
                minifyEnabled true // 设置代码进行混淆
                proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
                signingConfig signingConfigs.release
            }
        }
        addSigningProps(cdvReleaseSigningPropertiesFile, signingConfigs.release)
    }

可是并没有起作用，我故意在proguard-rules.pro里加一些错误的语法 也没有报错 ；
十分紧急，求大神指点！

Cordova Android项目如何做代码混淆 >> android

这个答案描述的挺清楚的：
http://www.goodpm.net/postreply/android/1010000006859381/CordovaAndroid项目如何做代码混淆.html