`require` ignores files with a `.`

[grilme99]

For example, if I have the following directory structure:

- example.lua
- example.spec.lua

And I have a script that requires "./example.spec", Lune will actually require example. This forces me to name my test files example_spec.lua, which goes against convention.

[filiptibell]

Fixed in 9ff142e for the next release, also added a test to make sure we don't regress on this