Prepare v2.8.4 release

  - Update CHANGELOG.md to reflect changes
  - Update version in mix.exs

Author: DavidAntaramian

CHANGELOG.md

@@ -7,6 +7,16 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+## [2.8.4] - 2018-08-14
+
+### Fixed
+
+  - The hostname caching released in v2.8.3 had the potential to crash the
+    Logger if an application was started between `:logger` and `:timber` _and_
+    made Logger calls. This was because the ETS table holding the cache had not
+    been started by Timber yet. To fix this, the hostname is now cached in the
+    application environment which is guaranteed to be available by that point.
+
 ## [2.8.3] - 2018-08-13
 
 ### Changed

mix.exs

@@ -9,7 +9,7 @@ defmodule Timber.Mixfile do
 
   @source_url "https://github.com/timberio/timber-elixir"
   @homepage_url "https://github.com/timberio/timber-elixir"
-  @version "2.8.3"
+  @version "2.8.4"
 
   # Project manifest for Mix
   #