hackney 4.8.6

Fixed

• Large HTTP/2 downloads over slow links no longer fail with
  {error, {stream_error, internal_error}}. hackney let only 64 KB of a
  response travel per round trip, so over a 120 ms link a 40 MB body took
  longer than the server allowed and the server cancelled it. HTTP/2
  downloads now run about as fast as HTTP/1.1 (#976).
• Closing a pooled TLS connection no longer logs a supervisor report with
  reason killed. The connection waited for the server to close its side,
  which took longer than the pool allows, and was killed (#976).

Changed

• Update h2 to 0.12.5 and certifi to 2.18.0. The new certifi removes
  the compromised eMudhra certificates from the CA bundle (#975).