[extensions-web] python: explicitly define message property since it is deprecated

[Yuri Konotopov <ykonotopov src gnome org>]

commit 873a4de92058025bd424bd8fcab44a520f5a174a
Author: Yuri Konotopov <ykonotopov gnome org>
Date:   Sat Dec 1 23:55:17 2018 +0400

    python: explicitly define message property since it is deprecated

 sweettooth/extensions/models.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/sweettooth/extensions/models.py b/sweettooth/extensions/models.py
index 7d0bd66..087e946 100644
--- a/sweettooth/extensions/models.py
+++ b/sweettooth/extensions/models.py
@@ -243,7 +243,9 @@ class ShellVersion(models.Model):
         return "%d.%d.%d" % (self.major, self.minor, self.point)
 
 class InvalidExtensionData(Exception):
-    pass
+    def __init__(self, message, *args):
+        super(InvalidExtensionData, self).__init__(message, *args)
+        self.message = message
 
 
 def parse_zipfile_metadata(uploaded_file):