Update project slick to 1.3.15
Merge pull request #2315 from jsdelivrbot/slick/1.3.15

Update project slick to 1.3.15
added js-xlsx
Add pako update.json
Merge pull request #2316 from zippy1981/js-xlsx

added js-xlsx
oops - fixed update.json
Merge pull request #2317 from as-com/pako/update.json

Add pako update.json