Ensure loadConfig returns the correct configuration when there are multiple configs

[davazp]

Fixes #390

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Fixes #390

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[hyoban]

I also found this problem and gave my fix in #389

[davazp]

Nice @hyoban, good timing.

I see, so your solution keeps a cache for each config.

Because the order file aren't processed isn't guaranteed with eslint, it's nice when files are processed alternatively from different projects. I left a comment in your PR to make it even more in that direction.

I'll keep mine around just in case, but I'm good if we focus on getting your fix merge.