fix: use common encode function across libraries

[jhosteny]

Ensure that we call a version of encode that exists for both the Jason library, and new builtin JSON module.

Fixes #98

[jhosteny]

Hi @maxmarcon. I am able to reproduce the bug in the library tests by adding the following to config/test.exs (with an updated version of elixir / erlang, of course):

config :phoenix, :json_library, JSON

I didn't put any test in, as I wasn't sure of how to accommodate both libraries easily, and the function is just missing.

[maxmarcon]

Hi @jhosteny thanks for the PR!

The built-in JSON module was introduced in Elixir 1.18 right? Then I think one way to test this is to:

1. add Elixir 1.18 to the Elixir versions we're testing in the CI
2. only configure the Jason as json_library if the Elixir version is < 1.18

1 is easy of course. Can 2 be done?

[jhosteny]

Hi @maxmarcon, thanks for taking a look! I added another commit which adds 1.18 to the CI matrix, and chooses JSON if it is version 1.18 or higher, and Jason otherwise.

If this looks okay, let me know if you'd like me to squash the commits.

[maxmarcon]

Thanks @jhosteny, this looks great! I'll merge and release a new version as soon as I get the chance

[maxmarcon]

🥳 🚀

[jhosteny]

Thank you so much @maxmarcon!

[maxmarcon]

Thanks to you! You created the MR 😄