handle basePath option for preprocessors paths

[ValentinH]

fix: handle basePath option for preprocessors paths

Closes #146

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[ValentinH]

I signed it!

[googlebot]

CLAs look good, thanks!

[dignifiedquire]

Thanks

[ValentinH]

When will it be released?

[dignifiedquire]

Now as 2.0.0

[ValentinH]

\o/ Just for my knowledge, why 2.0.0 and not 1.0.1?

[dignifiedquire]

Because while it is a bug fix, it's technically a breaking change to the behaviour in 1.0.0 so I went with a full major upgrade

[ValentinH]

Sounds good!