Laravel 5.1：验证失败后恢复旧输入

In Laravel 4 I could do something like:

    $rules = array(
                'first_name'    => 'required',
                'last_name'    => 'required',
                'email'    => 'required|email|unique:users',
                'username'    => 'required|alpha_dash|unique:users',
                'password' => 'required|min:5|confirmed',
            );
            $validator = Validator::make(Input::all(), $rules);
            if ($validator->fails())
            {
                return Redirect::to('register')
                    ->withErrors($validator)
                    ->withInput(Input::except('password'));
            }

In Laravel 5.1 it asks to do:

public function postRegister(Request $request){

        $rules = array(
            'first_name'    => 'required',
            'last_name'    => 'required',
            'email'    => 'required|email|unique:users',
            'password' => 'required|min:6',
        );
        $validator =  $this->validate($request, [
            'first_name'    => 'required',
            'last_name'    => 'required',
            'email'    => 'required|email|unique:users',
            'password' => 'required|min:6',
        ]);


    }

Blade File

@extends('...layouts.master')
    <div class="dt-form">
        <div class="errors">
            @if (count($errors) > 0)
                    <div class="alert alert-danger">
                        <ul>
                            @foreach ($errors->all() as $error)
                                <li>{{ $error }}</li>
                            @endforeach
                        </ul>
                    </div>
            @endif
        </div>
        <span class="main-heading">Sign up to DaysTime</span>
        <span class="sub-heading">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam at porttitor sem. Aliquam erat volutpat. Donec placerat.</span>
        {!! Form::open(array('action' => 'Auth\AuthController@postRegister','role'=>'form')) !!}
            <div class="form-group">
                {!! Form::label('first_name', 'First Name') !!}
                {!! Form::text('first_name', old('first_name'), array('class' => 'form-control','placeholder'=>'Enter your first name' )) !!}
            </div>

            <div class="form-group">
                {!! Form::label('last_name', 'Last Name') !!}
                {!! Form::text('first_name', Input::old('last_name'), array('class' => 'form-control','placeholder'=>'Enter your last name' )) !!}
            </div>
            <div class="form-group">
                {!! Form::label('email', 'Email Address') !!}
                {!! Form::email('email', Input::old('email'), array('class' => 'form-control','placeholder'=>'Enter your email address.' )) !!}
            </div>

            <div class="form-group">
                {!! Form::label('password', 'Password') !!}
                {!! Form::password('password',array('class' => 'form-control','placeholder'=>'Enter your password.' )) !!}
            </div>

            <div class="form-group">
                {!! Form::token() !!}
                {!! Form::submit("OK!!",array("class"=>"btn btn-lg btn-primary")) !!}
            </div>
        {!! Form::close() !!}
    </div>

Thing is,it is not restoring old value upon failed validation. How do I send it?

just replace redirect() with

Route::post('user/profile', function () {
    // Validate the request...

    return back()->withInput();
});

the docs explain it here