Update Elixir version

Update the project wide Elixir requirement to the latest stable version.

Additionally, update the OTP version in Travis to the latest one.

.travis.yml

@@ -1,11 +1,11 @@
 language: elixir
 elixir:
-  - 1.5.0
+  - 1.9.4
 notifications:
   recipients:
     - theavitex@gmail.com
 otp_release:
-  - 18.2
+  - 22.1
 env:
   - MIX_ENV=test
 script:

mix.exs

@@ -9,7 +9,7 @@ defmodule Glicko.Mixfile do
     do: [
       app: :glicko,
       version: "0.6.0",
-      elixir: "~> 1.5",
+      elixir: "~> 1.9",
       start_permanent: Mix.env() == :prod,
       deps: deps(),
       package: package(),