ReadTheDocs fix attempt #3

[ocket8888]

This fixes an incompatibility with the Sphinx version and the versions of other things as declared in the requirements.txt file for the docs. In the new version - 7.0.1 - there is now a lexer for application/x-www-form-urlencoded -encoded content, which means that some of our blocks that declare this type of content no longer lex. In reality, these payloads will actually be parsed as application/json no matter what's in the Content-Type header; Traffic Ops doesn't consider it at all. But it works equally well if you actually do set the correct header, and that gives us back syntax highlighting, so I fixed/changed those.

---

Which Traffic Control components are affected by this PR?

• Documentation

What is the best way to verify this PR?

Build the docs, make sure there are no warnings, even when you use the build tools declared by requirements.txt. Other than that, we need to wait for RTD to pick this up before we'll know if it has any effect on those issues.

If this is a bugfix, which Traffic Control versions contained the bug?

• master

PR submission checklist

• This PR doesn't need tests
• This PR is comprised of documentation changes
• This PR doesn't need a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY

[zrhoffman]

Looks promising