fixed spelling in validation message

fixed typo in auto-reorder validation message
diff --git a/erpnext/stock/doctype/item/item.py b/erpnext/stock/doctype/item/item.py
index 8321b3e..3b405c9 100644
--- a/erpnext/stock/doctype/item/item.py
+++ b/erpnext/stock/doctype/item/item.py
@@ -529,7 +529,7 @@
 			if d.get("warehouse") and d.get("warehouse") not in warehouse:
 				warehouse += [d.get("warehouse")]
 			else:
-				frappe.throw(_("Row {0}: An Reorder entry already exists for this warehouse {1}")
+				frappe.throw(_("Row {0}: A Reorder entry already exists for this warehouse {1}")
                                     .format(d.idx, d.warehouse), DuplicateReorderRows)
 
 			if d.warehouse_reorder_level and not d.warehouse_reorder_qty: