Pattern now matches fields with hyphens

[gudzpoz]

The original pattern would miss fields like 'content-length', which is used in Pleroma's signature.

However, when I went to check https://tools.ietf.org/html/rfc7230:

     header-field   = field-name ":" OWS field-value OWS

     field-name     = token

     token          = 1*tchar

     tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                    / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
                    / DIGIT / ALPHA
                    ; any VCHAR, except delimiters

it seems that the pattern could be further extended.
( But I do think that all headers nowadays will match [\w\s-] anyway :P )

[landrok]

LGTM Nice catch

I'll add a test to enforce that