Fix {plex_url) string formatting

plexpy/notification_handler.py

@@ -571,10 +571,8 @@ def build_notify_text(session=None, timeline=None, notify_action=None, agent_id=
     remaining_duration = duration - view_offset
 
     # Build Plex URL
-    metadata['plex_url'] = ('http://app.plex.tv/web/app#!/server/'
-                            + plexpy.CONFIG.PMS_IDENTIFIER
-                            + '/details/%2Flibrary%2Fmetadata%2F'
-                            + rating_key)
+    metadata['plex_url'] = 'http://app.plex.tv/web/app#!/server/{0}/details/%2Flibrary%2Fmetadata%2F{1}'.format(
+        plexpy.CONFIG.PMS_IDENTIFIER, str(rating_key))
 
     # Get media IDs from guid and build URLs
     if 'imdb://' in metadata['guid']: