laravel error mysql 5.5.55

[Illuminate\Database\QueryException]
  SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was t
  oo long; max key length is 767 bytes (SQL: alter table `users` add unique `
  users_email_unique`(`email`))

use Illuminate\Support\Facades\Schema;

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