Laravel: one to one relationship becomes one to many relationship

When I create a one-to-one relationship migration, laravel creates a one-to-many relationship.

PHP 7.1 & MySQL 5.7

The models are: Persona & User.

Persona:

public function user()
{
    return $this->hasOne('App\User', 'persona_id', 'id');
}

User:

public function persona()
{
    return $this->belongsTo('App\Persona', 'persona_id', 'id');
}

Migrations:

Schema::create('users', function (Blueprint $table) {
    $table->increments('id');
    $table->integer('persona_id')->unsigned();
    $table->foreign('persona_id')->references('id')->on('personas')->onDelete('cascade');
    $table->unique(['persona_id', 'id']);
    $table->string('email')->nullable()->unique();
    $table->string('password')->nullable();
    $table->rememberToken();
    $table->timestamps();
});


Schema::create('personas', function (Blueprint $table) {
    $table->increments('id');
    $table->string('tipo');
    $table->integer('cedula')->unsigned()->unique();
    $table->string('primer_nombre');
    $table->string('segundo_nombre')->nullable();
    $table->string('primer_apellido');
    $table->string('segundo_apellido')->nullable();
    /* Agregar demas campos que se requieran */
    $table->timestamps();
});

How can I make the relationship created in the database one by one and not one to many? Currently this is allowing me to save more than one user per person.

Thanks.

via Chebli Mohamed