message: fix invoice url response
diff: import * as fs from 'fs';
  import { Allocation, BankTransaction, BankTransfer, Contact, ContactGroup, CreditNote, Currency, Employee, ExpenseClaim, Invoice, Item, LinkedTransaction, ManualJournal, Payment, PurchaseOrder, Receipt, TaxRate, TrackingCategory, TrackingOption } from './AccountingAPI-models';
  -import { AccountsResponse, AllocationsResponse, AttachmentsResponse, BankTransactionsResponse, BankTransfersResponse, BrandingThemesResponse, ContactGroupsResponse, ContactsResponse, CreditNotesResponse, CurrenciesResponse, EmployeesResponse, ExpenseClaimsResponse, HistoryResponse, InvoiceRemindersResponse, InvoicesResponse, ItemsResponse, JournalsResponse, LinkedTransactionsResponse, ManualJournalsResponse, OrganisationResponse, OverpaymentsResponse, PaymentsResponse, PrepaymentsResponse, PurchaseOrdersResponse, ReceiptsResponse, RepeatingInvoicesResponse, ReportsResponse, TaxRatesResponse, TrackingCategoriesResponse, UsersResponse } from './AccountingAPI-responses';
  +import {
  + AccountsResponse,
  + AllocationsResponse,
  + AttachmentsResponse,
  + BankTransactionsResponse,
  + BankTransfersResponse,
  + BrandingThemesResponse,
  + ContactGroupsResponse,
  + ContactsResponse,
  + CreditNotesResponse,
  + CurrenciesResponse,
  + EmployeesResponse,
  + ExpenseClaimsResponse,
  + HistoryResponse,
  + InvoiceRemindersResponse,
  + InvoicesResponse,
  + ItemsResponse,
  + JournalsResponse,
  + LinkedTransactionsResponse,
  + ManualJournalsResponse,
  + OnlineInvoicesResponse,
  + OrganisationResponse,
  + OverpaymentsResponse,
  + PaymentsResponse,
  + PrepaymentsResponse,
  + PurchaseOrdersResponse,
  + ReceiptsResponse,
  + RepeatingInvoicesResponse,
  + ReportsResponse,
  + TaxRatesResponse,
  + TrackingCategoriesResponse,
  + UsersResponse
  +} from './AccountingAPI-responses';
  import { BaseAPIClient, XeroClientConfiguration } from './internals/BaseAPIClient';
  import { AccessToken, IOAuth1HttpClient } from './internals/OAuth1HttpClient';
  import { escapeString, generateQueryString } from './internals/utils';
  @@ -497,7 +529,7 @@ export class AccountingAPIClient extends BaseAPIClient {
  return this.oauth1Client.post<InvoicesResponse>(endpoint, invoices);
  },
  onlineInvoice: {
  - get: async (args?: { InvoiceID: string }): Promise<string> => {
  + get: async (args?: { InvoiceID: string }): Promise<OnlineInvoicesResponse> => {
  let endpoint = 'invoices';
  if (args && args.InvoiceID) {
  endpoint = endpoint + '/' + args.InvoiceID;
  