W3C CSP document moved to gihub.io URL [ci skip]

The old link https://dvcs.w3.org/hg/content-security-policy/raw-file/tip/csp-specification.dev.html is now being soft redirected to this new URL
Merge pull request #14612 from acallaghan/patch-1

W3C CSP document moved to gihub.io URL [ci skip]