README sample uses const instead of let when iterating paginated results

[doron2402]

Hi Square team 👋

In the Node.js SDK README, the pagination example uses:

const page = await client.bankAccounts.list();
while (page.hasNextPage()) {
    page = page.getNextPage();
}

However, this snippet will throw an error because page is declared as a const but then reassigned inside the loop

let page = await client.bankAccounts.list();
while (page.hasNextPage()) {
    page = page.getNextPage();
}

Thanks,