PHP: Laravel Cannot add foreign key constraint

I have files 2018_08_23_042408_create_roles_table.php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateRolesTable extends Migration
{
public function up()
{
    Schema::create('roles', function (Blueprint $table) {
        $table->increments('id');
        $table->string('role_name');
        $table->string('description');
        $table->timestamps();
    });
}
public function down()
{
    Schema::drop('roles');
}
}

and 2018_08_23_042521_create_users_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateUsersTable extends Migration
{
public function up()
{
    Schema::create('users', function (Blueprint $table) {
        $table->increments('id');
        $table->string('fullname');
        $table->string('email')->unique();
        $table->string('username')->unique();
        $table->string('password');
        $table->string('avatar_link');
        $table->integer('role_id');
        $table->foreign('role_id')->references('id')->on('roles');
        $table->rememberToken();
        $table->timestamps();
    });
}

public function down()
{
    Schema::table('role_user', function (Blueprint $table) {
        $table->dropForeign(['role_id']);
    });
    Schema::drop('users');
}
}

yet when I ran php artisan migrate I got this error

[Illuminate\Database\QueryException]                                         
 SQLSTATE[HY000]: General error: 1215 Cannot add foreign key 
 constraint (SQL  
: alter table `users` add constraint `users_role_id_foreign` foreign 
key (`role_id`) references `roles` (`id`))                                                                                                             

[PDOException]                                                          
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint 

And when I ran php artisan:reset it always shows error like 'Base table exists' and I have to run php artisan tinker and Schema::drop('users') to fix that. I have read similar question on stackoverflow but nothing worked. Any insight of what caused this? Thank you.

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