Allow the JSON library to load available variant

[chrisroberts]

Hi! I'm having some downstream issues due to the way the JSON library is getting
loaded in your code (sparkleformation/sfn#178). Due to other libraries also loading
JSON and the ext variant being available, both variants end up being loaded. As a result
TypeErrors are encountered:

• Replaced json dependency with json_pure. #19 (comment)

I tracked down an issue in the JSON repository (flori/json#269) that describes the
issue and from local testing it appears the underlying problem is a conflict between
the two implementations where each provides a subset of the entire functionality. The
result ends up being failures to generate JSON output depending on the data types. The
Fixnum type is an easy one to see fail.

From the documentation of the json project site (https://github.com/flori/json):

JSON first tries to load the extension variant. If this fails, the pure variant is loaded and used.

This is a bit more explanatory than the README file. Since the library will automatically
fallback to the pure variant if available, using require 'json' in both places is perfectly
acceptable to get the desired results. The loading bit can be seen here:

https://github.com/flori/json/blob/master/lib/json.rb#L57-L62

This would fix the issue for a number of downstream libraries and applications and
would be much appreciated to get merged and released when you can.

Thanks!

[luckymike]

👍 🙏

[trevorrowe]

Good catch. I'll cut a patch release shortly.

[chrisroberts]

Awesome, thanks so much!

[trevorrowe]

This is available in a 1.2.4 release.