Fix typo in build api endpoint

This corrects a copy-pasta typo from the previous loop.

Change-Id: If692a716a69f0fb7c48cc4c79a1704ea2847eeec

zuul/web/__init__.py

@@ -454,7 +454,7 @@ class ZuulWebAPI(object):
                 })
             for provides in build.provides:
                 ret['provides'].append({
-                    'name': artifact.name,
+                    'name': provides.name,
                 })
         return ret