Update references to RFC 2616 [SPR-12067]

[spring-projects-issues]

Sébastien Deleuze opened SPR-12067 and commented

Update references to the old RFC 2616 (HTTP 1.1) with references to the new RFC 7230, 7231, 7232, 7233, 7234 and 7235.

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Reference URL: https://www.mnot.net/blog/2014/06/07/rfc2616_is_dead

Issue Links:

• Improve HTTP support and update with new HTTP RFCs [SPR-11886] #16505 Improve HTTP support and update with new HTTP RFCs

Referenced from: commits 3922f6f