error 431 accepted due to rawdata in the payload

[Dancho80]

While forwarding the GitHub webhook payload to Jenkins, Jenkins responds with a 431 error. Upon investigation, it appears that the smee server is adding a rawdata header to the payload. In jenkins log you can see: jenkins org.eclipse.jetty.http.HttpParser parseFields Header is too large 8193>8192

proposal for a fix: https://github.com/probot/smee-client/pull/321