Use const in js examples

Created by: fulldecent

In the documentation at:

https://github.com/twbs/bootstrap/blob/f61a0218b36d915db80dc23635a9078e98e2e3e0/site/content/docs/5.0/examples/sidebars/sidebars.js#L2

https://github.com/twbs/bootstrap/blob/4d973259f55834ef9c9543fbcc265f11219ba8b2/site/content/docs/5.0/components/tooltips.md#example-enable-tooltips-everywhere

there are examples of using JavaScript to drive Bootstrap. That's great.

These use var where const can be more appropriate.

Recommending to prefer using const whenever possible.