fix #1107: re-enable scroll to anchor behavior

[janvennemann]

Summary

Re-eneable the scroll to anchor behavior in Vue router.

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
• Safari
• Edge
• IE

Other information:
Fixes #1107

[dimitrieh]

works 👍 but does not fix the problem noted at #1107 (comment) although that should, in that case, be scoped off to another issue 😉

[janvennemann]

@ulivz as per comments from #1075, handling the hash portion in scrollBehavior appearantly has some issues with the active header links plugin. I guess that is because the plugin constantly replaces the URL to get the sidebar updated.

Any plans how to proceed with these constant issues? We have made our own version of the active header links plugin which does not rely on route updates for a secondary sidebar we use. I can try and adopt that implementation into @vuepress/plugin-active-header-links

[ulivz]

This PR only solved a part of the problems, in fact, you can refer to the implementation of 0.x. but I can merge it first.