Update Clean.apk

The lib/ folder contains native libs so it must never be deleted.

https://github.com/appium/clean_apk/commit/af006af44b0c85006a8fa47c5fa3ab2cd6f40739

adb logcat -s "clean.apk" will display the debug log of clean.apk. This makes it
easy to find out if it's running successfully and what files are removed.

https://github.com/appium/clean_apk/commit/0445f7d0d1286c569c06e10d86bdcc1ad950688a
Merge pull request #1251 from bootstraponline/master

Update Clean.apk