message: Update docker image comment
diff: @@ -6,5 +6,4 @@ referenced in Cross.toml.
  [aarch64, x86_64]-unknown-linux-gnu
  -The `cross` docker image for x86_64-unknown-linux-gnu lacks libcap. The Dockerfile adds this.
  The Docker tag is referenced in Cross.toml.
  \ No newline at end of file
  