fix error in checkmap

src/c3nav/mapdata/packageio/write.py

@@ -95,7 +95,7 @@ def _write_object(obj, path, filename, prettify=False, check_only=False):
             print('- Created: '+os.path.join(path, filename))
 
     if check_only:
-        sys.stdout.write(difflib.unified_diff(
+        sys.stdout.writelines(difflib.unified_diff(
             [] if old_data is None else [(line+'\n') for line in old_data_encoded.split('\n')],
             [(line+'\n') for line in new_data_encoded.split('\n')],
             fromfiledate=timezone.make_aware(