title: unexpected token = for class properties in node 8.4
body: <p>running the following code in node (v8.4)</p>
  
  <pre><code>class TodoStore {
      todos = [];
  
      get completedTodosCount() {
          return this.todos.filter(
              todo =&gt; todo.completed === true
          ).length;
      }
  
      report() {
          if (this.todos.length === 0)
              return "&lt;none&gt;";
          return `Next todo: "${this.todos[0].task}". ` +
              `Progress: ${this.completedTodosCount}/${this.todos.length}`;
      }
  
      addTodo(task) {
          this.todos.push({
              task: task,
              completed: false,
              assignee: null
          });
      }
  }
  
  const todoStore = new TodoStore();
  
  todoStore.addTodo("read MobX tutorial");
  console.log(todoStore.report());
  
  todoStore.addTodo("try MobX");
  console.log(todoStore.report());
  
  todoStore.todos[0].completed = true;
  console.log(todoStore.report());
  
  todoStore.todos[1].task = "try MobX in own project";
  console.log(todoStore.report());
  
  todoStore.todos[0].task = "grok MobX tutorial";
  console.log(todoStore.report());
  </code></pre>
  
  <p>gives me the following error:</p>
  
  <pre><code>        todos = [];
                ^
  
  SyntaxError: Unexpected token =
      at createScript (vm.js:74:10)
      at Object.runInThisContext (vm.js:116:10)
      at Module._compile (module.js:537:28)
      at Object.Module._extensions..js (module.js:584:10)
      at Module.load (module.js:507:32)
      at tryModuleLoad (module.js:470:12)
      at Function.Module._load (module.js:462:3)
      at Function.Module.runMain (module.js:609:10)
      at startup (bootstrap_node.js:158:16)
      at bootstrap_node.js:598:3
  </code></pre>