Upgrade prettier

[TrySound]

Thanks for contributing to react-virtualized!

Here is a short checklist of additional things to keep in mind before submitting:

• Please make sure your pull request description makes it very clear what you're trying to accomplish. If it's a bug fix, please also provide a failing test case (if possible). In either case, please add additional unit test coverage for your changes. :)
• Run tests locally (npm test) to ensure that your change did not break linting or functionality.
• Be sure you have notifications setup so that you'll see my code review responses. (I may ask you to make some adjustments before merging.)

[codecov-io]

Codecov Report

Merging #924 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master    #924   +/-   ##
======================================
  Coverage    89.9%   89.9%           
======================================
  Files          57      57           
  Lines        1615    1615           
======================================
  Hits         1452    1452           
  Misses        163     163

Impacted Files	Coverage Δ
source/Grid/Grid.js	96.61% <ø> (ø)	⬆️
...e/Collection/utils/calculateSizeAndPositionData.js	92.3% <ø> (ø)	⬆️
source/Table/Table.js	89.28% <100%> (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 7af671d...64866ee. Read the comment docs.

[TrySound]

@bvaughn I would like to publish current master with latest fixes.

[TrySound]

It can be minor since I introduced .flow for WindowScroller

[bvaughn]

You want me to do a minor release to NPM? Happy to. Would you mind updating the CHANGELOG to reflect the changes first?