Spark 2.9.4

• Update Jetty to 9.4.33.v20201020 to fix CVE-2020-27216 <a href="https://github.com/perwendel/spark/pull/1201">#1201</a>
• added trustForwardHeaders method to decide if to trust HTTP forward headers <a href="https://github.com/perwendel/spark/pull/1197">#1197</a>
• Update to latest jetty version <a href="https://github.com/perwendel/spark/pull/1196">#1196</a>
• webSocketIdleTimeoutMillis should handle Long instead of Integer <a href="https://github.com/perwendel/spark/pull/1146">#1146</a>