fix compatibility with @babel/core v7

[maiis]

Issue:
When using babel v7-beta, this happens:

Module build failed: TypeError: Cannot read property 'loose' of undefined
    at _default (/Users/maiis/Projects/zip.ch/node_modules/@babel/plugin-proposal-class-properties/lib/index.js:20:23)
    at Function.memoisePluginContainer (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:113:13)
    at Function.normalisePlugin (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:146:32)
    at /Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:184:30
    at Array.map (<anonymous>)
    at Function.normalisePlugins (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:158:20)
    at OptionManager.mergeOptions (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:234:36)
    at OptionManager.init (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/options/option-manager.js:368:12)
    at File.initOptions (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/index.js:212:65)
    at new File (/Users/maiis/Projects/zip.ch/node_modules/@storybook/react/node_modules/babel-core/lib/transformation/file/index.js:135:24)

What I did

I moved babel-core to peerDependencies. This way babel-core is not installed again into @storybook/react/node_modules/

How to test

Use it with @babel7 dependencies and babel-bridge

  "devDependencies": {
    "@babel/core": "7.0.0-beta.35",
    "babel-core": "7.0.0-bridge.0",
    "@storybook/react": "3.2.17",
   ...
  }

[codecov]

Codecov Report

Merging #2494 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2494   +/-   ##
=======================================
  Coverage   16.87%   16.87%           
=======================================
  Files         307      307           
  Lines        7792     7792           
  Branches      780      780           
=======================================
  Hits         1315     1315           
- Misses       5863     5871    +8     
+ Partials      614      606    -8

Impacted Files	Coverage Δ
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/vue/src/server/babel_config.js	0% <0%> (-77.42%)	⬇️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
...b/ui/src/modules/ui/components/left_panel/index.js	18.51% <0%> (ø)	⬆️
addons/a11y/src/components/Tabs.js	0% <0%> (ø)	⬆️
app/react/src/demo/Button.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/components/search_box.js	32.94% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
...ents/src/manager/components/CommentsPanel/index.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/api/index.js	0% <0%> (ø)	⬆️
... and 44 more

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[Hypnosphi]

Please do the same for storyshots addon https://github.com/storybooks/storybook/blob/3b03c7e1b9b39f34b4fe3ac337bedd614eb73a75/addons/storyshots/package.json

[maiis]

@Hypnosphi done ✅

[Hypnosphi]

Thanks, will test