update link to 6.0 version of api doc

Author: AlexReutter

dataikuapi/dss/project.py

@@ -142,7 +142,7 @@ def get_metadata(self):
         Get the metadata attached to this project. The metadata contains label, description
         checklists, tags and custom metadata of the project.
 
-        For more information on available metadata, please see https://doc.dataiku.com/dss/api/5.0/rest/
+        For more information on available metadata, please see https://doc.dataiku.com/dss/api/6.0/rest/
         
         :returns: a dict object containing the project metadata.
         :rtype: dict