webpack sample updates (reactjs#1094)

* Update dependency react-helmet to v6

* Re-create webpack lockfile to avoid Node 12 issues

The error was: cannot find module @babel/compat-data/corejs3-shipped-proposals. smh

* Don't require exact 3.1.100 sdk

* Use asset manifest in webpack sample

* Fix public path in webpack sample

Fixes reactjs#1112

Co-authored-by: Renovate Bot <[email protected]>
Co-authored-by: Dustin Masters <[email protected]>

Author: 3 people