v5.6.2

• Avoid absorbing a panic in the case n.SendNotice() returns an error
  (#382)
• Fixed a SIGSEGV that may occur when a backlogged notice is sent
  (#352)
• Started handling HTTP response 429 from the Airbrake Notice API more
  granularly. Previously, we would return IP is rate limited whenever the
  Airbrake Notice API returned a 429. However, this response code may also
  indicate an error cap hit
  (#356)