feat: Requires Storybook@>=6.4

#120

To mitigate a deprecation for importing sub directory
(`addon-docs/blocks`). While that import is available from SB@6.3,
shape of `DocsContext` is changed at SB@6.4. Technically we can detect
the shape by checking property, but I decided to drop support SB@6.3 for
simplicity.

BREAKING CHANGE: Projects using SB@6.0<=x<6.4 needs to upgrade SB
version.

README.md

@@ -21,7 +21,7 @@ A [Storybook](https://github.com/storybooks/storybook) addon that embed Figma or
 
 ## Requirements
 
-- Storybook@>=6.0.0
+- Storybook@>=6.4.0
 
 This addon should work well with any framework: If you find the case the addon not works, please open an issue.
 

packages/storybook-addon-designs/package.json

@@ -37,11 +37,11 @@
     "typescript": "^4.7.3"
   },
   "peerDependencies": {
-    "@storybook/addon-docs": "^6.0.0",
-    "@storybook/addons": "^6.0.0",
-    "@storybook/api": "^6.0.0",
-    "@storybook/components": "^6.0.0",
-    "@storybook/theming": "^6.0.0"
+    "@storybook/addon-docs": "^6.4.0",
+    "@storybook/addons": "^6.4.0",
+    "@storybook/api": "^6.4.0",
+    "@storybook/components": "^6.4.0",
+    "@storybook/theming": "^6.4.0"
   },
   "scripts": {
     "dev": "tsc --watch --preserveWatchOutput",