Regression: core_urls: url 

Field mapping should be core_urls: url

Addresses https://github.com/joomla-extensions/weblinks/issues/19
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#### Copy from Issue

>The fix provided by Elin W has been applied several times now in Joomla core. Unfortunately it gets overrulled without properly documenting whether that is intentionally.

>Currently it is set to urls, which looks like the wrong value, it should be url.
If that is not a true statement it would help if somebody explains what the correct value should be!