...

import remark from 'remark';
import reactRenderer from 'remark-react';
import RemarkLowlight from 'remark-react-lowlight';

import js from 'highlight.js/lib/languages/javascript';

import githubSchema from 'hast-util-sanitize/lib/github.json';

const schema = Object.assign({}, githubSchema, {
  attributes: Object.assign({}, githubSchema.attributes, {
    code: [
      ...(githubSchema.attributes.code || []),
      'className'
    ]
  })
});

...
{remark().use(reactRenderer, {
  sanitize: schema,
  remarkReactComponents: {
    code: RemarkLowlight({
      js
    })
  }
}).processSync(readme).contents}
...