message: if `.dockerignore` doesn't exist, use `.gitignore`
diff: @@ -129,10 +129,14 @@ export async function docker(path, {
  const search = search_.map(file => asAbsolute(file, path))
  // compile list of ignored patterns and files
  + const dockerIgnore = await maybeRead(resolve(path, '.dockerignore'), null)
  +
  const filter = ignore().add(
  IGNORED +
  '\n' +
  - await maybeRead(resolve(path, '.dockerignore'))
  + clearRelative(dockerIgnore === null ?
  + await maybeRead(resolve(path, '.gitignore')) :
  + dockerIgnore)
  ).createFilter()
  const prefixLength = path.length + 1
  