'audio/x-flac' doesn't work

```
if 'audio/x-flac' not in get_filetype(f):
```
Previously this magic format is 'audio/x-flac'.The progarm will log something like below

```
[INFO] Skipped 'xxxxxxx.flac'
```
So I changed to
 ```
if 'audio/flac' not in get_filetype(f):
```
It does work.why,so strange?