update unstable url for: CARTA

[szjozsef]

update unstable url for: CARTA Chattanooga Area Regional Transportation Authority

update source: https://www.gocarta.org/about/developers-center/

[szjozsef]

what can be the reason for the failed checks ?
in the validation log it seems this feed is valid: feeds/gocarta.org.dmfr.json valid
but something else is failing....

feeds/openmobilityfoundation.github.com.dmfr.json invalid
[
  {
    instancePath: '/feeds/18',
    schemaPath: '#/required',
    keyword: 'required',
    params: { missingProperty: 'urls' },
    message: "must have required property 'urls'"
  }
]

[drewda]

The problem is now fixed by #853

After merging master into this branch, it should be fixed on this PR