Can not uninstall an app(hi app lock) which has device administrator rights
After viewing report's call stack, got to know that android.permission.SYSTEM_ALERT_WINDOW

for this app is not enabled. So, i enabled above setting by help of this link, https://www.experts-exchange.com/questions/28947878/How-to-enable-android-permission-SYSTEM-ALERT-WINDOW-in-marshmallow.html and then successfully revoke device administrator right and uninstalled it.