weather-service: Set contact_info to DOAP file URL

Currently, GNOME Calendar does not set up the contact_info needed in
libgweather 40 API. This leads to the following assertion, and no
weather forecast info being shown in Calendar:

`gweather_info_update: assertion 'info->contact_info != NULL' failed.`

To fix the assertion, set the URL to the DOAP file on the master branch.
GNOME Weather does the same, see:


Part of #682
1 job for gweather-contact-info in 4 minutes and 56 seconds