Chore: Check all webpack documentation links.

[ryan-roemer]

I think they have an update coming down the pipeline...

• https://twitter.com/thelarkinn/status/778403083143385088?refsrc=email&s=11
• https://github.com/webpack/webpack.js.org/pull/157

[paulathevalley]

The webpack v1 docs links are broken and need to be updated to point here: https://github.com/webpack/docs/wiki/contents

cc @formidableamy