Platform i386 removed from node alpine v12 & v14

[VonOx]

This nodejs/docker-node#1344

will break i386 build on node alpine v12 & v14 ( new lts ) based on manifest

docker manifest inspect -v library/node:12-alpine | jq '.[].Descriptor.platform'

{
  "architecture": "amd64",
  "os": "linux"
}
{
  "architecture": "arm",
  "os": "linux",
  "variant": "v6"
}
{
  "architecture": "arm",
  "os": "linux",
  "variant": "v7"
}
{
  "architecture": "arm64",
  "os": "linux",
  "variant": "v8"
}
{
  "architecture": "ppc64le",
  "os": "linux"
}
{
  "architecture": "s390x",
  "os": "linux"
}

This is not a problem for now with circlci because we do not use manifest ( of node-alpine ) for our multiarch build ( force pull arch specific )