Revert instructions to install v4 for now

Devin Torres · web-flow · commit a78814cb3f9e · 2017-06-13T18:34:07.000-05:00
diff --git a/README.md b/README.md
@@ -26,7 +26,7 @@ First, add Poison to your `mix.exs` dependencies:
 
 ```elixir
 def deps do
-  [{:poison, "~> 4.0"}]
+  [{:poison, "~> 3.1"}]
 end
 ```
 
