Implement HTTP Hijacker interface

[ribice]

Resolves #836

Was able to reproduce it with 0.28.0 (Error accepting websocket connection: failed to accept WebSocket connection: http.ResponseWriter does not implement http.Hijacker) and see it resolved with this fix.

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 81.98%. Comparing base (6d83e72) to head (4d07129).

Files	Patch %	Lines
http/wrap_writer.go	92.10%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #837      +/-   ##
==========================================
+ Coverage   81.76%   81.98%   +0.22%     
==========================================
  Files          50       51       +1     
  Lines        4436     4507      +71     
==========================================
+ Hits         3627     3695      +68     
- Misses        661      663       +2     
- Partials      148      149       +1     

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[ribice]

The only difference between this (and previous incomplete Wrapper) and Chi's is that this defaults to 200 instead of 0 if WriteHeader has not yet been called.

[kydemy-fran]

Is this fix working transparently? or requires some extra initialization?
I am still getting the error using the negronisentry package.

[ribice]

I just checked and it seems you're right, I've updated the implementation for stdlib but not for negroni. I'll submit a fix today.