[ts] Add missing signature for Customer.prototype.sendInvite()

Fixes: MONEI#464

Author: lpinca

index.d.ts

@@ -190,6 +190,10 @@ declare class Shopify {
     get: (id: number, params?: any) => Promise<Shopify.ICustomer>;
     list: (params?: any) => Promise<Shopify.ICustomer[]>;
     search: (params: any) => Promise<any>;
+    sendInvite: (
+      id: number,
+      params?: Shopify.ICustomerSendInvite
+    ) => Promise<Shopify.ICustomerSendInvite>;
     update: (id: number, params: any) => Promise<Shopify.ICustomer>;
     orders: (id: number, params?: any) => Promise<Shopify.IOrder[]>;
   };
@@ -1345,6 +1349,14 @@ declare namespace Shopify {
     updated_at: string;
   }
 
+  interface ICustomerSendInvite {
+    to: string;
+    from: string;
+    bcc: string[];
+    subject: string;
+    custom_message: string;
+  }
+
   type AllocationMethod = 'across' | 'each' | 'one';
   type TargetSelection = 'all' | 'entitled' | 'explicit';
   type TargetType = 'line_item' | 'shipping_line';