load requires a Loader arg in latest PyYAML

PyYAML 6.0 was released recently and the load method now requires a Loader argument (see yaml/pyyaml#561 and yaml/pyyaml#576). Can either provide one like this (I think it's backwards compatible with version 5) or could pin the version of PyYAML in requirements.txt.

start_zk_cluster.py

@@ -6,7 +6,7 @@
 template = jinja_environment.get_template('zoo.cfg.template')
 
 with open('config.yaml') as f:
-    config = yaml.load(f)
+    config = yaml.load(f, Loader=yaml.SafeLoader)
 
 hosts = [(k, v) for k, v in config['hosts'].items()]