api更新

当对framework开发之后，一些新的api我们需要更新对应的current.txt文件。

To make these errors go away, you have two choices:
   1) You can add "@hide" javadoc comments to the methods, etc. listed in the
      errors above.

   2) You can update current.txt by executing the following command:
         make update-api

      To submit the revised current.txt to the main Android repository,
      you will need approval.

对应的MTK的项目，我们需要执行的make update-api时要加上项目名称
例如：
make g255_base update-api
或
./mk g255_base update-api