[1.3] add pyyaml dep to setup.py

Author: jgrewe

setup.py

@@ -12,7 +12,7 @@
 with open('README.rst') as f:
     description_text = f.read()
 
-install_req = ["lxml"]
+install_req = ["lxml", "pyyaml"]
 if sys.version_info < (3, 4):
     install_req += ["enum"]