App: Query Wikimedia Commons API over HTTPS

The request to Wikimedia Commons API was failing because it was
trying to load content from an insecure URL.

The error message was:

The page at 'https://tools.wmflabs.org/wm-metrics/category-induced'
was loaded over HTTPS, but ran insecure content from
'http://commons.wikimedia.org/w/api.php?callback=...':
this content should also be loaded over HTTPS.