Error gray-matter cannot find a parser for: ----

[willdurand]

https://sentry.io/tailordev-oss/monod/issues/164738209/

Error: gray-matter cannot find a parser for: ----
...
  at _this4 (./app/components/Preview/presenter.jsx:175:31)
  at render (./app/components/Preview/presenter.jsx:181:16)
  at loadSuccess (./app/modules/documents.js:27:4)
  at loadSuccess (./app/modules/documents.js:54:15)
...
(45 additional frame(s) were not displayed)