refactor, better class namespace intergration

app/Models/Shop/Offer.php

@@ -14,16 +14,16 @@ class Offer extends Model
     
     public function article()
     {
-        return $this->belongsTo('App\Models\Shop\Article');
+        return $this->belongsTo(Article::class);
     }
 
     public function variation()
     {
-        return $this->belongsTo('App\Models\Shop\Variation');
+        return $this->belongsTo(Variation::class);
     }
 
     public function tariff()
     {
-        return $this->belongsTo('App\Models\Shop\Tariff');
+        return $this->belongsTo(Tariff::class);
     }
 }