added accept argument to force wav file

Author: mnr

examples/text_to_speech_v1.py

@@ -11,7 +11,7 @@
 print(json.dumps(text_to_speech.voices(), indent=2))
 
 with open(join(dirname(__file__), '../resources/output.wav'), 'wb') as audio_file:
-    audio_file.write(text_to_speech.synthesize('Hello world!'))
+    audio_file.write(text_to_speech.synthesize('Hello world!',accept='audio/wav',voice="en-US_AllisonVoice"))
 
 print(json.dumps(text_to_speech.pronunciation('Watson', pronunciation_format='spr'), indent=2))