Fixed underline

src/zc/buildout/buildout.txt

@@ -1135,7 +1135,8 @@ macros. In particular, the variable substitutions are performed
 relative to the myfiles section.
 
 Extending sections (macros) - Adding and removing options
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+---------------------------------------------------------
+
 We can also add and remove options in extended sections.
 
 This is illustrated below; first we define a base configuration.