环境：
Android Studio 3.2 + macOS High Sierra 10.13.6
已科学上网
报错信息：
Unable to find valid certification path to requested target
Caused by: org.gradle.api.resources.ResourceException: Could not get resource 'https://dl.google.com/dl/android/maven2/com/android/tools/build/gradle/3.2.1/gradle-3.2.1.pom'
经过一番排查，最终确认是开了 Charles Proxy 造成的问题
解决方法：
1. 关闭 Charles Proxy
2. 重启 Android Studio
参考：
https://stackoverflow.com/questions/26697118/android-studio-unable-to-find-valid-certification-path-to-requested-target
