Update less to 3.5+

[hsn10]

We should update less to at least 3.5 to get newer features, specially maps are nice.

After update there are 4 tests failing, most likely related to fact that paths are now normalized to have forward slash in name, tested on node 10.16

[rsese]

Thanks @hsn10 - can you explain in more detail how this would be useful for Atom? We're not currently in a place to take on changes for use cases outside of Atom so we need to confirm whether the update is doing something like fixing a specific bug or solving a specific problem within Atom.

[abaracedo]

I'm with @hsn10 and I will point to upgrade it to the latest stable version as there're bug fixes (the changelog doesn't mention which ones) and lots of functionalities.

IMHO it can improve the performance and it will give us better options to write better styles.

[hsn10]

I am using maps in my CSS design. It allows me to generate different themes from the basic one with simple change.

[abaracedo]

Another thing that came to my mind, this module allows caching less code into css but I see there's a problem.

If I would like to use this module in a different project that's using less I won't be able to use it if the version that my project depends on is v3 or greater. Shouldn't less be a dependency of the project that uses this module?