v2.6.0

• Gracefull shutdown of HTTP server. (#439, @miry)
• Support PATCH HTTP method for Proxy update(PATCH /proxies/{proxy}) and
  Toxic update(PATCH /proxies/{proxy}/toxics/{toxic}) endpoints.
  Deprecat POST HTTP method for those endpoints. (@miry)
• Client does not parse response body in case of errors for Populate.
  Requires to get current proxies with new command. (#441, @miry)
• Client specifies User-Agent HTTP header for all requests as
  "toxiproxy-cli/ /".
  Specifies client request content type as application/json. (#441, @miry)
• Replace Api.Listen parameters host and port with single addr. (#445, @miry)