v0.86.1

• Update RocksDB to 6.7.3, and Go to 1.14.2, along with many other package dependencies.
• The etcdtest package no longer embeds an Etcd server. Instead, an etcd
  binary must be available on the PATH and is invoked as a sub-process,
  using Unix domain sockets. Users who use etcdtest themselves, or are running
  Gazette tests outside of the hermetic Docker build environment, must provide a
  reasonably recent version of etcd.
• Relatedly, the gazette client package no longer depends on Etcd (including the Etcd client).
• JSON-framed messages are now able to use custom marshal/demarshal routines.
• gazctl journals/shards apply now interprets revision -1 (previously
  disallowed) to mean "don't care", allowing specs to be applied which will always
  overwrite what's in Etcd.
  This makes sense for specs managed in another source-of-truth (eg, git).
• Mitigations and improved logging for issue GH-248.
• Remove explicit TCP keep-alive management, as this is now Go default.
• Various doc improvements & cleanups.