我尝试将Onesignal作为推送服务添加到应用程序，但现在我在编辑build.gradle文件后收到以下错误。
错误：无法获取类型为org.gradle.api.Project的根项目“android”的未知属性“android”。
有人能告诉我怎么解决这个问题吗？这是我第一次编辑android项目。
这是我的build.gradle（应用程序）文件：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28

    defaultConfig {
        minSdkVersion 16
        targetSdkVersion 28
        applicationId "io.gonative.android.azndpe"
        versionCode 2

        manifestPlaceholders = [manifestApplicationId: "${applicationId}",
                                onesignal_app_id: "APP-ID",
                                onesignal_google_project_number: "REMOTE"]
    }

    signingConfigs {
        release {
            storeFile file("../../release.keystore")
            storePassword "password"
            keyAlias "release"
            keyPassword "password"
        }
        upload {
            storeFile file("../../upload.keystore")
            storePassword "password"
            keyAlias "upload"
            keyPassword "password"
        }
    }

    buildTypes {
        debug {
            applicationIdSuffix ".debug"
        }
        releaseApk {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-project.txt'
            zipAlignEnabled true
            signingConfig signingConfigs.release
        }
        releaseAppbundle {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-project.txt'
            zipAlignEnabled true
            signingConfig signingConfigs.upload
        }
    }

    flavorDimensions "webview"

    productFlavors {
        normal {
            dimension "webview"
        }
    }
}

dependencies {
    implementation 'com.joanzapata.iconify:android-iconify-fontawesome:2.2.2'
    implementation 'com.facebook.android:facebook-android-sdk:4.39.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.android.support:customtabs:28.0.0'
    implementation 'com.android.support:support-v4:28.0.0'
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.google.android.gms:play-services-gcm:12.0.1'
    implementation 'com.google.android.gms:play-services-location:12.0.1'
    implementation 'com.onesignal:OneSignal:[3.9.1, 3.99.99]'
    implementation fileTree(dir: 'libs', include: '*.jar')
    implementation fileTree(dir: 'libs', include: '*.aar')

}