旧时工程build.gradle的改变

compile 改为 implementation
provided 改为 
compile project(':library') 改为 implementation project(':library')
testCompile 'junit:junit:4.12' 
改为
testImplementation 'junit:junit:4.12'
androidTestCompile 改为 androidTestImplementation
compile fileTree(include: ['*.jar'], dir: 'libs')
改为
implementation fileTree(dir: 'libs', include: ['*.jar','*.aar'])

其它
minSdkVersion 改 minSdk
targetSdkVersion 改 targetSdk

apply plugin: 'com.android.application'
apply plugin: 'com.android.library'
改成
plugins {
id 'com.android.application'
id 'com.android.library'
//或
//id 'com.android.application' version '7.2.1' apply false
//id 'com.android.library' version '7.2.1' apply false
}
instrumentTest 改成 androidTest

参考：

https://zhuanlan.zhihu.com/p/44371449