Import react with star import

[anajavi]

Apparently the way forward with importing react is by:

import * as React from 'react';

For reference: facebook/react#18102

I find the syntax a little odd, but apparently it makes better webpack builds also:
https://twitter.com/sebmarkbage/status/1250284377138802689

In the future, the import can be dropped altogether, but I guess that at least the peerDependency of react needs to be bumped. Which means major release.

This PR is just to be forward compatible. No breaking changes here.

[codecov-commenter]

Codecov Report

Merging #292 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #292   +/-   ##
=======================================
  Coverage   88.29%   88.29%           
=======================================
  Files          82       82           
  Lines        1051     1051           
  Branches      203      203           
=======================================
  Hits          928      928           
  Misses        107      107           
  Partials       16       16           

Impacted Files	Coverage Δ
...highcharts/src/components/Annotation/Annotation.js	88.23% <ø> (ø)
...s/react-jsx-highcharts/src/components/Axis/Axis.js	90.47% <ø> (ø)
...x-highcharts/src/components/BarSeries/BarSeries.js	100.00% <ø> (ø)
...x-highcharts/src/components/BaseChart/BaseChart.js	97.77% <ø> (ø)
...x-highcharts/src/components/ColorAxis/ColorAxis.js	100.00% <ø> (ø)
...react-jsx-highcharts/src/components/Debug/Debug.js	22.22% <ø> (ø)
.../components/Highcharts3dChart/Highcharts3dChart.js	80.00% <ø> (ø)
.../src/components/HighchartsChart/HighchartsChart.js	100.00% <ø> (ø)
...ponents/HighchartsSparkline/HighchartsSparkline.js	42.10% <ø> (ø)
...x-highcharts/src/components/Options3d/Options3d.js	92.00% <ø> (ø)
... and 20 more

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