run CI on elixir 1.11

Author: lukaszsamson

.travis.yml

@@ -30,8 +30,10 @@ matrix:
       elixir: 1.8.2
     - otp_release: 22.3
       elixir: 1.9.4
-    - otp_release: 23.0.3
-      elixir: 1.10.3
+    - otp_release: 23.0.4
+      elixir: 1.10.4
+    - otp_release: 23.1.1
+      elixir: 1.11.1
       env:
         - CHECK_FORMATTED=1
         - RUN_DIALYZER=1