font paths in production are wrong

i run `npm run ionic:build -- --prod`, then copy `www` on a dockerfile, which just servers it.

When I try to access my app, I get a `404` for `../build/assets/fonts/ionicons.woff2?v=3.0.0-alpha.3`. Looking at the `www` folder, this is obvious. The fonts are in `../assets/fonts`, not `../build/assets/..`.