Update version compatibility table

Author: whitfin

.travis.yml

@@ -51,18 +51,26 @@ matrix:
       otp_release: 19.3
     - elixir: 1.10
       otp_release: 18.3
+    - elixir: 1.9
+      otp_release: 23.0
     - elixir: 1.9
       otp_release: 19.3
     - elixir: 1.9
       otp_release: 18.3
+    - elixir: 1.8
+      otp_release: 23.0
     - elixir: 1.8
       otp_release: 19.3
     - elixir: 1.8
       otp_release: 18.3
+    - elixir: 1.7
+      otp_release: 23.0
     - elixir: 1.7
       otp_release: 18.3
     - elixir: 1.6
       otp_release: 23.0
+    - elixir: 1.6
+      otp_release: 23.0
     - elixir: 1.6
       otp_release: 22.3
     - elixir: 1.6