Add missing quote

Author: allanrenucci

docs/docs/internals/syntax.md

@@ -326,7 +326,7 @@ DefDef            ::=  DefSig [‘:’ Type] ‘=’ Expr
                     |  ‘this’ DefParamClause DefParamClauses                    DefDef(_, <init>, Nil, vparamss, EmptyTree, expr | Block)
                        (‘=’ ConstrExpr | [nl] ConstrBlock)
 
-TmplDef           ::=  ([‘case’] ‘class’ | trait’) ClassDef
+TmplDef           ::=  ([‘case’] ‘class’ | ‘trait’) ClassDef
                     |  [‘case’] ‘object’ ObjectDef
                     |  ‘enum’ EnumDef
 ClassDef          ::=  id ClassConstr TemplateOpt                               ClassDef(mods, name, tparams, templ)