Larabel迁移文件发生错误怎么办？

Illuminate\Database\QueryException  : 
SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; 
max key length is 1000 bytes (SQL: alter table `users` add unique `users_email_unique`(`email`))

<?php

namespace App\Providers;use Illuminate\Support\ServiceProvider;use Illuminate\Support\Facades\Schema;class AppServiceProvider extends ServiceProvider{
    public function register()
    {
    }

    public function boot()
    {
        Schema::defaultStringLength(191);
    }}

Schema::defaultStringLength(191);