imgtool: fix package's author email

Fix author email after move to new mailing list.

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/scripts/setup.py b/scripts/setup.py
index 058d0cb..bf35d9f 100644
--- a/scripts/setup.py
+++ b/scripts/setup.py
@@ -5,7 +5,7 @@
     name="imgtool",
     version=imgtool_version,
     author="The MCUboot committers",
-    author_email="dev-mcuboot@lists.runtime.co",
+    author_email="mcuboot@groups.io",
     description=("MCUboot's image signing and key management"),
     license="Apache Software License",
     url="http://github.com/JuulLabs-OSS/mcuboot",