[setup] Upgrade to pyyaml 3.13

Author: mpsonntag

setup.py

@@ -28,7 +28,7 @@
 with open('README.rst') as f:
     description_text = f.read()
 
-install_req = ["lxml", "pyyaml==3.12", "rdflib", "docopt"]
+install_req = ["lxml", "pyyaml==3.13", "rdflib", "docopt"]
 
 if sys.version_info < (3, 4):
     install_req += ["enum34"]