Add number of offers in amazon

Create one more function that using to return the number of sellers

Author: hqtoan94

amazon/api.py

@@ -1378,6 +1378,15 @@ def detail_page_url(self):
             DetailPageURL (string)
         """
         return self._safe_get_element_text('DetailPageURL')
+    
+    @property
+    def number_sellers(self):
+        """Number of offers - New.
+
+        :return:
+            Number of offers - New (string)\
+        """
+        return self._safe_get_element_text('OfferSummary.TotalNew')
 
 
 class AmazonCart(LXMLWrapper):