[FIX] theme_avantgarde: properly define 3rd 3-cols image for previews

Since [1], the manifest is not well formed: it contains a duplicated key

[1]: odoo@08befbe

closes odoo#697

X-original-commit: a26fec8
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_avantgarde/__manifest__.py

@@ -20,7 +20,7 @@
         'website.s_picture_default_image': '/theme_avantgarde/static/src/img/pictures/bg_image_14.jpg',
         'website.s_three_columns_default_image_1': '/theme_avantgarde/static/src/img/pictures/bg_image_15',
         'website.s_three_columns_default_image_2': '/theme_avantgarde/static/src/img/pictures/bg_image_16.jpg',
-        'website.s_three_columns_default_image_2': '/theme_avantgarde/static/src/img/pictures/bg_image_17.jpg',
+        'website.s_three_columns_default_image_3': '/theme_avantgarde/static/src/img/pictures/bg_image_17.jpg',
         'website.s_text_image_default_image': '/theme_avantgarde/static/src/img/pictures/bg_image_13.jpg',
     },
     'snippet_lists': {