actix-server: v2.0.0-beta.6

• Add io-uring feature for enabling async file I/O on linux. #374
• Server no long listens to SIGHUP signal. Previously, the received was not used but did block
  subsequent exit signals from working. #389
• Remove config module. ServiceConfig, ServiceRuntime public types are removed due to
  this change. #349
• Remove ServerBuilder::configure #349