targetUrl field missing

Storage loader's sql assets have targetUrl but not the json schema
Merge branch 'patch-1' of https://github.com/gisripa/snowplow into gisripa-patch-1
Merge branch 'gisripa-patch-1' into feature/0.9.7-new
StorageLoader: added missing targetUrl field to ad_impression JSON Path file, thanks @gisripa! (fixes #951)