Merge pull request scala#4570 from marconilanna/patch-1

Traits mistakenly set as 'Case Classes' subsection

Author: SethTisue

spec/05-classes-and-objects.md

@@ -964,7 +964,7 @@ This form of extensibility can be excluded by declaring the base class
 directly extend `Expr` must be in the same source file as
 `Expr`.
 
-### Traits
+## Traits
 
 ```ebnf
 TmplDef          ::=  `trait' TraitDef