Appease lint

lithp · lithp · commit fce995809849 · 2019-12-10T15:49:15.000-08:00
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,
