Prevent CDN caching your updated JavaScript files

TL;DR

extract some value from the file that changes with its content --like content's md5, or modified timestamp-- and append it to the file name

for example, let's say "index.js" and its md5 is "30c2234" (shortened for readability)

later when you modify the file, the hash change, and clients start to request the new one.

this allows to set cache's evict time in doomsday