Tap-shopify

* Correct abandoned_checkouts schema to correctly reflect some properties as arrays [44](https://github.com/singer-io/tap-shopify/pull/44)

1.3.3.
* Add `build` to the list of fields we canonicalize for the Transactions stream [103](https://github.com/singer-io/tap-shopify/pull/103)

* Add `python_requires` to `setup.py` [101](https://github.com/singer-io/tap-shopify/pull/101)
* We've tested the tap on `python 3.5.2` and `python 3.8.0`

* Canonicalize `Timestamp` to `timestamp` on `Transactions.receipt` [98](https://github.com/singer-io/tap-shopify/pull/98)

This version ships both [96][PR96] and [97][PR97].

From [97][PR97]:
* removes the "untestable streams" list from all tests.
* makes the test match the tap and expect the default page size to be 175, not 250
* adds bookmarking to order_refunds
* adds bookmarking to transactions
* adds shopify error handling to transactions
* The tests would fail with unhandled 429s
* adds pagination to transactions

From [96][PR96]:
* Update the API version from `2020-10` to `2021-04`

[PR97]: https://github.com/singer-io/tap-shopify/pull/97/
[PR96]: https://github.com/singer-io/tap-shopify/pull/96

* Add `null, object` to customer schema definition [94](https://github.com/singer-io/tap-shopify/pull/94)

* Bumps `singer-python` from `5.11.0` to `5.12.1` [91](https://github.com/singer-io/tap-shopify/pull/91)