fix the title in audio extractor doc

doc/guide_audio_extractor.rst

-==========
-User guide
-==========
+=========================
+Audio Embedding Extractor
+=========================
 
 This subpackage is part of ``bob.learn.pytorch``  package to extract features from an input audio using CNN models which 
 trained with pytorch_.
@@ -26,7 +26,7 @@ DltResNet Model
 
 
 ResNet Model
----------------
+------------
 
 
 :ref:`bob.bio.base <bob.bio.base>` wrapper ResNet model.