升級Android Studio使用的Gradle爲最新的版本

項目下build.gradle的內容如下：

buildscript {
    ext.kotlin_version = '1.2.71'
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

升級 Android Studio 的Gradle插件版本，把鼠標放到 classpath 'com.android.tools.build:gradle: 這行，如果當前的插件不是最新版本的話，IDE會提示當前該插件的最新版本號，將本配置中的 3.2.1 換成3.5.2，將鼠標放到 org.jetbrains.kotlin:kotlin-gradle-plugin 這行，會提示kotiin最新的插件版本，將 ext.kotlin_version 這個值，設置爲當前的最新版本即可，如果不設置這個就會報如下的類似錯誤：

WARNING: API 'variant.getJavaCompile()' is obsolete and has been replaced with 
'variant.getJavaCompileProvider()'.
It will be removed at the end of 2019.
For more information, see https://d.android.com/r/tools/task-configuration-avoidance

按照當前最新版本修改：
com.android.tools.build:gradle 最新版本爲 3.5.2
gradle 的最新版本爲 6.0

注意com.android.tools.build:gradle 插件 並不能支持所有的Gradle版本，可以去官網查看，某個版本的com.android.tools.build 支持哪些版本的Gradle,
https://developer.android.google.cn/studio/releases/gradle-plugin.html#updating-plugin

org.jetbrains.kotlin:kotlin-gradle-plugin 最新版本爲 1.3.50

同時把Gradle的倉庫修改爲阿里雲的倉庫，防止某些衆所周知的原因造成，下載更新失敗。

修改後版內容如下：

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/repository/central' }
        maven { url 'https://maven.aliyun.com/repository/gradle-plugin' }
        maven { url 'https://maven.aliyun.com/repository/public' }
        maven { url 'https://maven.aliyun.com/repository/releases' }
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.2'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/repository/central' }
        maven { url 'https://maven.aliyun.com/repository/gradle-plugin' }
        maven { url 'https://maven.aliyun.com/repository/public' }
        maven { url 'https://maven.aliyun.com/repository/releases' }
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

將gradle-wrapper.properties中的

distributionUrl=https://services.gradle.org/distributions/gradle-4.2.4-all.zip

修改爲：
distributionUrl=https://services.gradle.org/distributions/gradle-6.0-all.zip