prettier: Flow parser on Node v6 causes Segmentation Fault

Hi! This is an issue showing up in Draft.js CI runs.

We enabled Prettier as part of our Travis CI runs on Github recently - in https://github.com/facebook/draft-js/commit/cd20b992d4b054d70f756c258e5e75e518995e12

During CI we currently install the most recent compatible version of any dependency automatically, and so we started pulling in v1.9.0 and then v1.9.1 when those were released 6 days ago.

At that time we started seeing CI failing due to a segmentation fault when it runs the eslint check, which is the step that runs prettier.

I verified that disabling prettier or downgrading to v1.8.* does not lead to the segmentation fault - see https://github.com/facebook/draft-js/pull/1567

I have not dug into the Prettier codebase so I’m not sure what could be happening to cause a segmentation fault, but I’m happy to provide any info or help that I can. We’d like to keep using Prettier in Draft.js, and get the goodies in new releases.

Thanks for creating such a powerful and useful tool! 📐✨💕