Add newline between projects in std output format

Without this it is very difficult to visually distinguish between
the project outputs.

Change-Id: I452aa5500bda1bf607ba11baa92be3377945a4ab

openstack_releases/cmds/list_unreleased_changes.py

@@ -119,6 +119,7 @@ def generate_output(content, output_format='std',
             out.append(range_msg)
             if repo['commits'].get('logs', None):
                 out.append("\n".join(repo['commits']['logs']))
+            out.append('')
         return '\n'.join(out)