Gitlab was added as an option for webhook. Documentation should be updated accordingly.

Where: Chapter 2, paragraph: "The BuildConfig object definition..."
Modification:

• "which is either a GitHub or Generic webhook" -> "which is either a GitHub, GitLab or Generic webhook"
• "that enables the rebuilding of images when the webhook is triggered by Git or GitHub" ->
  "that enables the rebuilding of images when the webhook is triggered."