Android Error:Annotation processors must be explicitly declared now. The following dependencies on

异常：

Annotation processors must be explicitly declared now.  The following dependencies on the compile classpath are found to contain annotation processor.  Please add them to the annotationProcessor configuration.
- butterknife-7.0.1.jar (com.jakewharton:butterknife:7.0.1)
Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior.  Note that this option is deprecated and will be removed in the future.
See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

解决办法：
在app的build中

android {
    ...
    defaultConfig {
        ...
        //添加如下配置就OK了
        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
    }
    ...
}