升级Android Studio使用的Gradle为最新的版本

项目下build.gradle的内容如下：

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
}

升级 Android Studio 的Gradle插件版本，把鼠标放到 classpath 'com.android.tools.build:gradle: 这行，如果当前的插件不是最新版本的话，IDE会提示当前该插件的最新版本号，将本配置中的 3.2.1 换成3.5.2，将鼠标放到 org.jetbrains.kotlin:kotlin-gradle-plugin 这行，会提示kotiin最新的插件版本，将 ext.kotlin_version 这个值，设置为当前的最新版本即可，如果不设置这个就会报如下的类似错误：

WARNING: API 'variant.getJavaCompile()' is obsolete and has been replaced with 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

按照当前最新版本修改：
com.android.tools.build:gradle 最新版本为 3.5.2
gradle 的最新版本为 6.0

注意com.android.tools.build:gradle 插件 并不能支持所有的Gradle版本，可以去官网查看，某个版本的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 最新版本为 1.3.50

同时把Gradle的仓库修改为阿里云的仓库，防止某些众所周知的原因造成，下载更新失败。

修改后版内容如下：

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
}

将gradle-wrapper.properties中的

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

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