chore: migrate storybook to v6 (#741)

* chore: migrate storybook to v6

* chore: bump the storybook version to v6.3

Author: koba04

.storybook/config.js

@@ -1,6 +1,7 @@
 const { plugins, rules } = require('webpack-atoms');
 
 module.exports = {
+  stories: ['../stories/index.js'],
   webpackFinal: (config) => {
     config.module = {
       rules: [rules.js(), rules.astroturf(), rules.css({ extract: false })],

.storybook/main.js

@@ -0,0 +1,9 @@
+import React from 'react';
+
+export const decorators = [
+  (Story) => (
+    <React.StrictMode>
+      <Story />
+    </React.StrictMode>
+  ),
+];

.storybook/preview.js

@@ -76,8 +76,8 @@
     "@semantic-release/git": "^9.0.0",
     "@semantic-release/github": "^7.0.5",
     "@semantic-release/npm": "^7.0.5",
-    "@storybook/addon-actions": "^5.3.18",
-    "@storybook/react": "^5.3.18",
+    "@storybook/addon-actions": "^6.3.4",
+    "@storybook/react": "^6.3.4",
     "@typescript-eslint/eslint-plugin": "^4.26.1",
     "astroturf": "^0.10.4",
     "babel-eslint": "^10.1.0",