Add API Versioning configuration

[anduong]

Description

Add API version configuration to ShopifyAPI

Context

We have all setup for API key, Password, Shop domain, etc. However, Shopify API still requires us to specify the API version to make request using the correct API version. I think we should make this as a configuration to make it more convenient.

This will also help to fix this issue #7

Proposed Solution

The configuration for API version will either

• Use the API version specified by user input
• Automatically find the latest version to set as default if the user does not specify the input. The latest version is automatically figured out by selecting the last API version released quarterly by Shopify according to https://shopify.dev/api/usage/versioning and https://shopify.dev/api/admin/graphql/reference/common-objects/queryroot#publicapiversions-2021-07 (Add API Versioning configuration #22 (comment))

What changes in this PR

• Add prompt to ask for API version
• Implement a mechanism to automatically figure out the latest API version using the current date & time
• Add test to make sure the latest API version mechanism working correctly with every month in a year
• Update Shopify API, GraphQL and GraphQL client gems to the latest
• Update README to let people know how to configure the API version
• Add webmock to test the HTTP Request as fakeweb is no longer maintained

[anduong]

Hi @chrisbutcher and @pfeffer, could you please help to review this PR?

[chrisbutcher]

This is a neat trick!

But that said, while stable API versions typically do get released on the first of the month/quarter, sometimes (as with version 2020-07) the version was released a day later).

Perhaps a safer alternative to computing the version handle in this library would be:

Since you have the shop domain + API credentials from above, perhaps you should call the GraphQL Admin API to obtain the latest API version from https://shopify.dev/api/admin/graphql/reference/common-objects/queryroot#publicapiversions-2021-07.

The last supported: true version would be the one to pick here.

[anduong]

Hi @chrisbutcher,

Thanks for reviewing the changes. It is good to know that we can query the supported API version. Your suggestion is better than the time-induction approach. It helps to avoid timing sensitivity (especially in different timezones).

I will implement the GraphQL query and update this PR soon

[anduong]

@chrisbutcher I have updated the implementation to get the Public API versions from Shopify. Can you please review the change? Thanks

One small note is that I am using webmock instead of fakeweb to test the functionality as the gem fakeweb is no longer maintained. See chrisk/fakeweb#62 and chrisk/fakeweb#57

[chrisbutcher]

Thanks @anduong !