Cannot handle GBK character when build javadoc

Before Issue

1. Please search on the Issues
2. Please search on the wiki
3. Please set FileDownloadLog.NEED_LOG=true and review the Logcat output from main process and :filedownloader process ( pay attention to Warn and Error level logcat)

Issue

D:\github\FileDownloader\library\src\main\java\com\liulishuo\filedownloader\BaseDownloadTask.java:577: error: unmappable character for encoding GBK
         *             {@link FileDownloadStatus#completed}銆亄@link FileDownloadStatus#warn}銆?
                                                                                            ^
D:\github\FileDownloader\library\src\main\java\com\liulishuo\filedownloader\services\BaseFileServiceUIGuard.java:156: error: unmappable character for encoding GBK
            // 瀵圭О,鍙湁涓?娆emove锛岄槻姝㈠唴瀛樻硠婕?
                       ^
D:\github\FileDownloader\library\src\main\java\com\liulishuo\filedownloader\services\BaseFileServiceUIGuard.java:156: error: unmappable character for encoding GBK
            // 瀵圭О,鍙湁涓?娆emove锛岄槻姝㈠唴瀛樻硠婕?
                                         ^
3 errors

FAILURE: Build failed with an exception.

1. What problem do you get?
   Cannot handle GBK character when build javadoc

2. Which version of FileDownloader are you using when you produce such problem?
   latest master

3. How to reproduce such problem?
   just fire gradlew.bat build from Windows

4. Do you set FileDownloadLog.NEED_LOG=true?

5. Could you please reproduce this problem and provide all main process and :filedownloader process logcat

6. Can you fix it by yourself and request PR, if not, what's problem do you get when you try to fix it
   The GBK character in javadoc should be removed for better compatibility.

P.S. If you don't know how to get :filedownloader process, it's recommended to using pidcat to just filter all your application logcat, or define process.non-separate=true on filedownloader.properties

请在Issue前认真的跟进上面提到的建议，这样将可以极大的加快你遇到问题的处理。

Start with library/src/main/java/com/liulishuo/filedownloader/BaseDownloadTask.java and library/src/main/java/com/liulishuo/filedownloader/services/BaseFileServiceUIGuard.java, where the Windows GBK javadoc build reports unmappable characters. Run gradlew.bat build on Windows and verify that the javadoc compilation completes without encoding errors.