fix nav url change bug (#865)

[KyleJShaver]

Summary
Fixes issue #865 wherein if the bottom element is too small, navigating to the hash will cause the url to change to the element displayed at the top of the page. For example:

The Problem:

Note how clicking on "Advanced Configuration" causes the "Insert Code Snippets" navigation item to be selected and hash to be reflected in the URL

Fixed:

Note how clicking on "Advanced Configuration" remains selected

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:

If changing the UI of default theme, please provide the before/after screenshot:

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

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

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

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:
The added logic only kicks in if the user is navigating to the very bottom of the page.

[ulivz]

LGTM, Thanks