A change to the "delete secret" machine API format

[Tim_Newsham]

We’re pushing out a change to the machines API endpoint for deleting secrets: DELETE https://api.machines.dev/v1/apps/$FLY_APP_NAME/secrets/$SECRETNAME . Previously the result on success was HTTP status 204 with no body. Going forward it will be HTTP status 200 with a JSON body containing the updated secrets min_version, as in {"Version": 1234}