Create cache_dir if not exists

[kangfend]

get_file doesn't save gender_detection.model to cache_dir if directory doesn't exists

[arunponnusamy]

Hey @kangfend , Thanks for the PR. Will test this and merge.

[arunponnusamy]

I have figured out the issue. I should have used cache_subdir with absolute path instead of cache_dir. Replacing cache_dir with cache_subdir in the below line fixes the issue. Thanks for reporting this.

model_path = get_file("gender_detection.model", dwnld_link,
                              cache_subdir= os.path.expanduser('~') + os.path.sep + '.cvlib' + os.path.sep + 'pre-trained')