Updated incorrect documentation link for maintenance policies (#590)

Author: ezilber-akamai

linode_api4/groups/maintenance.py

@@ -14,7 +14,7 @@ def maintenance_policies(self):
         Returns a collection of MaintenancePolicy objects representing
         available maintenance policies that can be applied to Linodes
 
-        API Documentation: https://techdocs.akamai.com/linode-api/reference/get-policies
+        API Documentation: https://techdocs.akamai.com/linode-api/reference/get-maintenance-policies
 
         :returns: A list of Maintenance Policies that can be applied to Linodes
         :rtype: List of MaintenancePolicy objects as MappedObjects