[error fix]You have not accepted the license agreements of the following SDK components

在MAC的環境下，如果ionic2 在加入platform或build時出現以下的問題，先檢查『Android SDK Platform 24』是否真的有安裝，如果確定有，請確認『ANDROID_HOME=/usr/local/opt/android-sdk』下有『licenses』的目錄，如果沒有，請去SDK下載目錄下拷貝過去，或是 ln 過去

* What went wrong:

A problem occurred configuring root project 'android'.

> You have not accepted the license agreements of the following SDK components:

  [Android SDK Platform 24].

  Before building your project, you need to accept the license agreements and complete the installation of the missing components using the Android Studio SDK Manager.

  Alternatively, to learn how to transfer the license agreements from one workstation to another, go to http://d.android.com/r/studio-ui/export-licenses.html