sign.py: fix issues reported by pycodestyle

Adds missing blank line.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/scripts/sign.py b/scripts/sign.py
index ad47479..84fd771 100755
--- a/scripts/sign.py
+++ b/scripts/sign.py
@@ -4,6 +4,7 @@
 #
 # SPDX-License-Identifier: BSD-2-Clause
 
+
 def uuid_parse(s):
     from uuid import UUID
     return UUID(s)