Fix: Update acorn to 6.4.0 to fix several issues

[sergdenisov]

This acorn update to 6.4.0 version should fix issues like:

• Unexpected token in code example #1321;
• Error: import or require() statements can be added only by editing a Markdown #1312;
• How can I import 'antd' or any other lib ? #1278;
• [Regression v8 to v9] Example can't import itself anymore. moduleAliases/WebpackConfig.resolve.alias is broken => import or require() statements can be added only by editing a Markdown example file #1310.

More about acorn@6.4.0 — https://github.com/acornjs/acorn/releases/tag/6.4.0.

[styleguidist-bot]

🎉 This PR is included in version 10.3.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[craigkovatch]

This introduced huge breaks for us: #1527