Test on several Elixir version on travis

Signed-off-by: chatgris <julien@stormz.me>

Author: chatgris

.travis.yml

@@ -1,10 +1,14 @@
 language: erlang
 otp_release:
   - 17.0
+  - 17.1
+env:
+  - ELIXIR="v0.14.3"
+  - ELIXIR="v0.15.0"
 install: mix deps.get
 before_install:
   - mkdir -p vendor/elixir
-  - wget -q http://s3.hex.pm/builds/elixir/stable.zip && unzip -qq stable.zip -d vendor/elixir
+  - wget -q https://github.com/elixir-lang/elixir/releases/download/$ELIXIR/Precompiled.zip && unzip -qq Precompiled.zip -d vendor/elixir
   - export PATH="$PATH:$PWD/vendor/elixir/bin"
   - export MIX_ENV=test
   - mix local.hex --force