adds a single comma to appease black

ESultanik · ESultanik · commit 440821247231 · 2020-07-23T14:03:34.000-04:00
diff --git a/polytracker/cfg.py b/polytracker/cfg.py
@@ -13,7 +13,7 @@
     Optional,
     Set,
     TypeVar,
-    Union
+    Union,
 )
 
 import graphviz
