Table get out of sync

[johanwilson]

Environment

• Package version(s): @blueprintjs/table: 3.8.0, @blueprintjs/core: 3.19.0,
• Browser and OS versions: Electron, Chrome & Win 10

If possible, link to a minimal repro:
https://codesandbox.io/s/blueprint-sandbox-0dbiw

Steps to reproduce

Play around with the slider to see how the tabel get out of sync with numRows.
Seems to affect Slider too.

Resizable has a minior error

Warning: Resizable: Did not properly initialize state during construction. Expected state to be an object, but it was undefined.

And a component has been forgotten

react-dom.development.js:12466 Warning: componentWillUpdate has been renamed, and is not recommended for use. See https://fb.me/react-unsafe-component-lifecycles for details.
Please update the following components: TableBodyCells

Actual behavior

This will lead to Attempt to read an array index that is out of bounds if it was a real array

Expected behavior

Table stays in sync with numRows