* [PHP] Correctly format JSON in headers
`ObjectSerializer::toHeaderValue()` in the generated PHP code calls
`toString()` on the values, which formats JSON with the `JSON_PRETTY_PRINT`
option. This will result in a multi-line header which cannot be parsed
since linebreaks aren't allowed by RFC 7230.
In my case I have a header schema called `UpdateUser` which I had hoped
would be serialized as `{"type":"staff","id":123}`.
Every single `__toString()` in the generator does the same thing, so I
figured it's safe to change `toHeaderValue()` to convert to JSON directly,
without `JSON_PRETTY_PRINT`. This fix works for me.
* More sensible approach to providing a header value
* Just strip the newlines
* Go back to previous solution
60567bddd6