Service Worker precache_urls should respect --relative

[frnco]

Currently it seems pretty much all URLs are properly relativized when --relative is set, except for the precache_urls used in the serviceworker. The relevar file is mint/src/utils/service_worker.cr, in line 21, inside the function precache_urls. Using #321 as a reference it seems it's just a matter of using that same path_for() function instead of just concatenating the initial /.
The current code:

    def precache_urls
      files
        .join(",\n") do |file|
          %('/#{file.relative_to(DIST_DIR)}')
        end
    end

I believe the change would result in something like:

    def precache_urls
      files
        .join(",\n") do |file|
          path_for(file.relative_to(DIST_DIR))
        end
    end

Is it really that simple or did I miss something? If it is, I believe it could be pretty useful when relative paths are needed.