fix: redirect any github 404 to our custom 404 page

[zebateira]

Closes #388

This should fix the 404 gibhub page showing.
@terichadbourne what we discussed regarding redirecting valid urls to hash urls would be a bit more tricky (e.g. /tutorials -> /#/tutorials) since it would still rely on the 404 hack #393

[terichadbourne]

@zebateira To attempt to proof this one I used:

npm run build
npm install -g serve
serve -s dist

I got it running from dist but http://localhost:5000/404 redirects to http://localhost:5000/404#/ which is the homepage, not http://localhost:5000/#/404, our custom 404 page. I’m happy to assume this is a weird testing limitation and just merge and check when it’s live if you’re confident it’s set up as needed. Let me know what you recommend.

[zebateira]

@terichadbourne weird behaviour from serve. I used this and it worked as it should:

npm run build && npx http-server dist -p 3000

[terichadbourne]

Working perfectly now!