Fix author_email UNKNOWN in pip show

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/scripts/setup.py b/scripts/setup.py
index a58e6b0..707f60d 100644
--- a/scripts/setup.py
+++ b/scripts/setup.py
@@ -5,6 +5,7 @@
     name="imgtool",
     version=imgtool_version,
     author="The MCUboot commiters",
+    author_email="None",
     description=("MCUboot's image signing and key management"),
     license="Apache Software License",
     url="http://github.com/JuulLabs-OSS/mcuboot",