Missing dependencies for Gunicorn.

requirements.txt

 sqlalchemy==1.3.13
 Flask==1.1.1
+Flask-Caching=1.8.0
 Flask-SQLAlchemy==2.4.1
 Flask-RESTful==0.3.8
 flask-marshmallow==0.11.0
@@ -14,4 +15,5 @@ validators==0.12.1
 simplejson==3.17.0
 accessify==0.3.1
 librosa==0.7.2
-gunicorn==20.0.4
\ No newline at end of file
+gunicorn==20.0.4
+pyyaml-5.3.1
\ No newline at end of file