unable to use relative paths in cairoPath

[Th0rgal]

Hey there,

I would like to add "./lib" as a cairoPath for all my projects because this is what I use for all protostar projects, but I can only put absolute path.

[ericglau]

Feel free to submit a PR if you'd like. Relevant part of code is here. When adding the cairoPath elements, if an element is a relative path, it could be made absolute by appending to each workspaceFolder as additional paths entries (similar to what is being done for sourceDir).