Add text/markdown to MediaType [SPR-14192]

[spring-projects-issues]

Venil Noronha opened SPR-14192 and commented

I've added text/markdown entry to MediaType as per https://tools.ietf.org/html/rfc7763.

I've signed the ICLA. Please review and pull.

Thanks,
Venil Noronha

---

Reference URL: #1041

Referenced from: commits b2c9c8a