Fixed scrollbars appearing when they're not needed

[Narcha]

When a table has fixedHeader enabled and not enough entries to fill it's max-height, a disabled scrollbar appears.
I fixed this by replacing overflow-y: scroll with overflow-y: auto so the scrollbar only appears when it's necessary.

I've tested a few other configurations to see if this change breaks anything,
I'm not aware of any negative impact this could have.
Please let me know if I missed anything.

[codecov]

Codecov Report

Merging #767 (ad5d0c7) into master (c33175e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #767   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files          43       43           
  Lines         490      490           
  Branches      138      138           
=======================================
  Hits          487      487           
  Misses          3        3           

Impacted Files	Coverage Δ
src/DataTable/TableBody.js	100.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c33175e...ad5d0c7. Read the comment docs.

[jbetancur]

Thank you for PRing this. Sorry for the delay, but I still need some time to test it out. Also, we will need to PR this into the next branch as well.

[jbetancur]

This looks good! I'll also cherry pick this change into the next branch as well

[Narcha]

One thing to note:
If #586 gets fixed by somehow adding the correct amount of padding-right to rdt_TableHeadRow to compensate for the scrollbar width, this will have to be reevaluated.

[jbetancur]

@Narcha I've moved #586 to next as well. I've been meaning to fix that issue for some time