added method to allowe remove item using product_id

Author: bhavinjr

README.md

@@ -100,6 +100,14 @@ To remove users all wishlist item, specify the user_id.
 Wishlist::removeUserWishlist(1);
 ```
 
+### Wishlist::removeByProduct()
+
+To remove particular product using product_id, specify the product_id and user_id respectively.
+
+```php
+Wishlist::removeByProduct(15, 1);
+```
+
 
 ### Wishlist::count()
 

src/Wishlist.php

@@ -39,6 +39,11 @@ public function removeUserWishlist($user_id)
     	$this->instance->ofUser($user_id)->delete();
     }
 
+    public function removeByProduct($product_id,$user_id)
+    {
+        $this->getWishlistItem($product_id,$user_id)->delete();
+    }
+
     protected function create($product_id,$user_id)
     {
     	$matchThese	=   ['product_id'   =>  $product_id,'user_id' => $user_id];