Fixed hash anchor scrolling

[f0rr0]

Fixes #462

[KyleAMathews]

This is great! Thanks for tracking down the problem and fixing it! Could you land the same change on the 1.0 branch?

It'd be on both https://github.com/gatsbyjs/gatsby/blob/1.0/lib/intermediate-representation-dir/production-app.js and https://github.com/gatsbyjs/gatsby/blob/1.0/lib/intermediate-representation-dir/root.js (root.js needs renamed but it's the development web-entry.js basically.)

[f0rr0]

@KyleAMathews Anytime! Opened a PR for the 1.0 branch. It'll be great if you could cut a new release from master though.

[f0rr0]

It's worth noting that the back button scrolling will not work for hash anchors on the same page. Could cause confusion for someone.

[jlengstorf]

Hiya @f0rr0! 👋

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