Allow i18n.mjs instead of i18n.js

[MonstraG]

What version of this package are you using?
2.6.2

What problem do you want to solve?
run with Deno

What do you think is the correct solution to this problem?
Deno forces you to use modules, I have no choice

Are you willing to submit a pull request to implement this change?
Not certain.

[aralroca]

Probably we need to support both. PR are welcome, this is the current code:

https://github.com/aralroca/next-translate-plugin/blob/99c1faefcd7167a7caa309f2affc7d0d807a76e4/src/index.ts#L38