[gobject-introspection] docwriter: Fix Exception message attribute

[Christoph Reiter <creiter src gnome org>]

commit 551a3f77816b89b540cdca6836c2822ac4740adb
Author: Philip Chimento <philip chimento gmail com>
Date:   Sat Apr 6 14:17:12 2019 -0700

    docwriter: Fix Exception message attribute
    
    This may have been a leftover from Python 2. Exception('message') does
    not automatically set a message attribute on the exception object.

 giscanner/docwriter.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/giscanner/docwriter.py b/giscanner/docwriter.py
index aa8b993c..786da80d 100644
--- a/giscanner/docwriter.py
+++ b/giscanner/docwriter.py
@@ -1209,7 +1209,7 @@ class DevDocsFormatterGjs(DocFormatterGjs):
         try:
             return super(DevDocsFormatterGjs, self).to_underscores(node)
         except Exception as e:
-            if e.message == 'invalid node':
+            if e.args[0] == 'invalid node':
                 print('warning: invalid node in', node.parent.name,
                     file=sys.stderr)
                 return node.parent.name + '_invalid_node'