Fix error on countries source id

[jsanz]

Fixes #198

When creating the new World Countries layer I used the same source identifier, which made the v2 manifest to point to a blob that contains the TopoJSON version of the dataset.

To check this PR works the simplest way is to see that the staging manifest for v2 points to the GeoJSON dataset

$ curl -s --compressed https://storage.googleapis.com/elastic-bekitzur-emsfiles-vector-dev/v2/manifest\?elastic_tile_service_tos\=agree\&my_app_name\=ems-landing\&my_app_version\=7.2.0\&license\=643c1faf-80fc-4ab0-9323-4d9bd11f4bbc | jq '.layers[0].url'
"https://storage.googleapis.com/elastic-bekitzur-emsfiles-vector-dev/blob/5659313586569216?elastic_tile_service_tos=agree"

$ curl -s --compressed "https://storage.googleapis.com/elastic-bekitzur-emsfiles-vector-dev/blob/5659313586569216?elastic_tile_service_tos=agree" | jq '.features[0].properties'
{
  "name": "Antigua and Barbuda",
  "iso2": "AG",
  "iso3": "ATG"
}

[nickpeihl]

just one nit, but otherwise lgtm!

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request