Add "extract_features=False" to broken example

[LinusOstlund]

The following example doesn't work:

from musicnn.extractor import extractor
taggram, tags = extractor('./audio/joram-moments_of_clarity-08-solipsism-59-88.mp3', model='MTT_musicnn') ~~~~

Since the extract_features parameter defaults to True, it produces a "too many values to unpack" error. Explicitly setting extract_features=False fixes the example.