fix some problems

app/MedicalCenter.php

@@ -7,10 +7,12 @@ use Illuminate\Database\Eloquent\Model;
 class MedicalCenter extends Model
 {
     public $fillable = ['name', 'city_id', 'address', 'phone_number'];
+
     public function users()
     {
         return $this->hasMany('App\User');
     }
+
     public function city()
     {
         return $this->belongsTo('App\City');