message: docs: fix typo in glossary
  Add missing comma  in structural directive section that made dash display incorrectly.
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diff: @@ -867,7 +867,7 @@ To learn more, see [Introduction to Services and Dependency Injection](guide/arc
  ## structural directives
  -A category of [directive](#directive) that is responsible for shaping HTML layout by modifying the DOM&mdashthat is, adding, removing, or manipulating elements and their children.
  +A category of [directive](#directive) that is responsible for shaping HTML layout by modifying the DOM&mdash;that is, adding, removing, or manipulating elements and their children.
  To learn more, see [Structural Directives](guide/structural-directives).
  