Merge branch 'fix_block_context' into 'master'

Specification change: Fix asciidoctor block context.

See merge request gitlab-org/gitlab-ce!22280

doc/administration/integration/plantuml.md

@@ -80,10 +80,10 @@ our AsciiDoc snippets, wikis and repos using delimited blocks:
 
     ```
     [plantuml, format="png", id="myDiagram", width="200px"]
-    --
+    ----
     Bob->Alice : hello
     Alice -> Bob : Go Away
-    --
+    ----
     ```
 
 - **reStructuredText**