Update 'yconf' dependency to fix Erlang/OTP 19.x

mix.exs

@@ -102,7 +102,7 @@ defmodule Ejabberd.Mixfile do
      {:ex_doc, ">= 0.0.0", only: :dev},
      {:eimp, "~> 1.0"},
      {:base64url, "~> 0.0.1"},
-     {:yconf, git: "https://github.com/processone/yconf", ref: "9e700d7307310fcbd1293ac82f1b45cf6e6ef7e8"},
+     {:yconf, git: "https://github.com/processone/yconf", ref: "60e431a1f1e4504ccc9e329a9202b88c26b341ae"},
      {:jose, "~> 1.8"},
      {:idna, "~> 6.0"},
      {:p1_acme, "~> 1.0"}]

rebar.config

@@ -27,7 +27,7 @@
 	{idna, ".*", {git, "https://github.com/benoitc/erlang-idna", {tag, "6.0.0"}}},
         {xmpp, ".*", {git, "https://github.com/processone/xmpp", {tag, "1.4.7"}}},
         {fast_yaml, ".*", {git, "https://github.com/processone/fast_yaml", {tag, "1.0.25"}}},
-	{yconf, ".*", {git, "https://github.com/processone/yconf", "9e700d7307310fcbd1293ac82f1b45cf6e6ef7e8"}},
+	{yconf, ".*", {git, "https://github.com/processone/yconf", "60e431a1f1e4504ccc9e329a9202b88c26b341ae"}},
         {jiffy, ".*", {git, "https://github.com/davisp/jiffy", {tag, "1.0.4"}}},
         {p1_oauth2, ".*", {git, "https://github.com/processone/p1_oauth2", {tag, "0.6.6"}}},
         {pkix, ".*", {git, "https://github.com/processone/pkix", {tag, "1.0.5"}}},