Blockquotes fail to nest

[dHannasch]

Blockquotes fail to nest. This can be seen from #120 --- viewing https://github.com/dHannasch/gatsby-starter-morning-dew/blob/nested-blockquote/content/posts/2018-01-03-Big-Sample-Post/index.md#blockquotes on GitHub shows how the blockquotes are supposed to nest, but when you gatsby build, the inner blockquotes are lost.

This is probably going to need to be raised as an issue on gatsby-plugin-mdx or gatsby-transformer-remark or somewhere, but in the meantime it would be good if we can figure out what combination of options is causing the problem to manifest on this particular starter.