JavaScript example: Fix parsing of statements

Fixes a problem where statements starting with a reserved word produced
errors like this:

  Reserved word "return" can't be used as an identifier.

The problem was in a wrong ordering of choices in the |Statement| rule
together with aggressive reserved word detection in the |Identifier|
rule.

examples/javascript.pegjs

@@ -993,18 +993,23 @@ Statement
   = Block
   / VariableStatement
   / EmptyStatement
-  / ExpressionStatement
   / IfStatement
   / IterationStatement
   / ContinueStatement
   / BreakStatement
   / ReturnStatement
   / WithStatement
-  / LabelledStatement
   / SwitchStatement
   / ThrowStatement
   / TryStatement
   / DebuggerStatement
+  /*
+   * The following two statements begin with identifiers. They must be at the
+   * very end of the list to prevent triggering reserved word detection in the
+   * |Identifier| rule by keywords the statemets above begin with (e.g. |if|).
+   */
+  / ExpressionStatement
+  / LabelledStatement
 
 Block
   = "{" __ body:(StatementList __)? "}" {