這是gradle版本原因造成的，如果不想升級gradle版本到2.3.2以上，需要使用原來低版本的方法。

Gradle DSL method not found: 'google()'
Possible causes:<ul><li>The project 'BottomNavigation' may be using a version of the Android Gradle plug-in that does not contain the method (e.g. 'testCompile' was added in 1.1.0).
Upgrade plugin to version 2.3.2 and sync project</li><li>The project 'BottomNavigation' may be using a version of Gradle that does not contain the method.
Open Gradle wrapper file</li><li>The build file may be missing a Gradle plugin.

Apply Gradle plugin</li>

解決辦法：將google()修改為：

//        google()
maven {
            url 'https://maven.google.com/'
name 'Google'
}

Gradle DSL method not found: 'testImplementation()'
Possible causes:<ul><li>The project 'BottomNavigation' may be using a version of the Android Gradle plug-in that does not contain the method (e.g. 'testCompile' was added in 1.1.0).
Upgrade plugin to version 2.3.2 and sync project</li><li>The project 'BottomNavigation' may be using a version of Gradle that does not contain the method.
Open Gradle wrapper file</li><li>The build file may be missing a Gradle plugin.

Apply Gradle plugin</li>

解決辦法：將testImplementation修改為testCompile

將implementation修改為compile

androidTestImplementation修改為androidTestCompile