Fixed addon knobs proptypes deserialization

[Gongreg]

Issue: #1265

What I did

Fixed proptype.
Deserialization doesn't return array anymore.

How to test

https://github.com/jkempff/storybook-addon-knobs-proptypes-issue .

[codecov]

Codecov Report

Merging #1290 into master will not change coverage.
The diff coverage is 50%.

@@           Coverage Diff            @@
##           master    #1290    +/-   ##
========================================
  Coverage   13.76%   13.76%            
========================================
  Files         201      201            
  Lines        4620     4620            
  Branches      501      609   +108     
========================================
  Hits          636      636            
+ Misses       3545     3456    -89     
- Partials      439      528    +89

Impacted Files	Coverage Δ
addons/knobs/src/components/types/Date/index.js	72.72% <ø> (ø)	⬆️
addons/knobs/src/components/types/Array.js	80% <ø> (ø)	⬆️
addons/knobs/src/components/types/Object.js	5.81% <0%> (ø)	⬆️
addons/knobs/src/components/types/Boolean.js	11.62% <100%> (ø)	⬆️
addons/info/src/components/Node.js	0% <0%> (ø)	⬆️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
...rc/modules/ui/components/left_panel/text_filter.js	33.33% <0%> (ø)	⬆️
addons/info/src/components/PropVal.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/types/Number.js	8.06% <0%> (ø)	⬆️
addons/knobs/src/components/types/Select.js	7.93% <0%> (ø)	⬆️
... and 28 more

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[shilman]

@Gongreg would you mind adding some examples to the examples/cra-kitchen-sink project to test this out?

[Gongreg]

@shilman, is the example project created by user is not enough? :)

[shilman]

@Gongreg if it's checked in we can test it automatically in the near future

[Gongreg]

@shilman, ah, makes sense, I will just not be able to do that in the next few days.

[shilman]

@Gongreg OK I'll just add it and merge then

[shilman]

LGTM!