Fix code block in environment documentation

What does this MR do?

This MR changes a line in the gitlab-ci documentation about environments.

Before this MR, the environment documentation looks like this:

and a little later

The second part doesn't make sense, I think, if the first code example looks the same. This MR changes the first code block to look like this:

deploy to production:
  stage: deploy
  script: git push production HEAD:master
  environment: production

which I think makes more sense together with the text.