Appease lint

lithp · lithp · commit f4a6d664b4d9 · 2019-12-10T15:56:52.000-08:00
diff --git a/eth/db/chain.py b/eth/db/chain.py
@@ -35,6 +35,7 @@
     GENESIS_PARENT_HASH,
 )
 from eth.exceptions import (
+    CanonicalHeadNotFound,
     HeaderNotFound,
     ReceiptNotFound,
     TransactionNotFound,
