Logger instance can't register log folder when user provide optional param

[hemulin]

So,
The Logger.instance() is able to receive an optional param of log_dir.
The problem is that in the code you can find those lines:

self.__log_dir = log_dir

if self.__log_dir is None:
    self.__LOG_DIR = self.__app_dirs.logs()
AppDirs.mkdir(self.__LOG_DIR)

While I believe it should be:

self.__log_dir = log_dir

if self.__log_dir is None:
    self.__LOG_DIR = self.__app_dirs.logs()
else:
    self.__LOG_DIR = self.__log_dir
AppDirs.mkdir(self.__LOG_DIR)

[legion0]

feel free to create a pull request for this, look like a simple change :)