Update TravisCI configuration (#241)

Author: amatalai

.travis.yml

@@ -1,21 +1,19 @@
 language: elixir
 elixir:
-  - 1.5.1
-  - 1.6.5
+  - 1.8.2
 sudo: false # to use faster container based build environment
 notifications:
   recipients:
     - [email protected]
 otp_release:
-  - 19.3
-  - 20.0
+  - 22.0
 script:
   - if [[ $(elixir --version) = *"1.6"* ]]; then mix format --check-formatted; fi
   - mix test
 after_script:
   - mix deps.get --only docs
   - MIX_ENV=docs mix inch.report
 matrix:
-  exclude:
-    - elixir: 1.3.4
-      otp_release: 20.0
+  include:
+    - elixir: 1.5.1
+      otp_release: 19.3