Add OTP 21.3 to the Travis matrix

Author: tompave

.travis.yml

@@ -4,15 +4,13 @@ elixir:
   - 1.7
   - 1.6
 otp_release:
+  - 21.3
   - 21.2
   - 21.1
-  - 21.0
   - 20.3
   - 20.2
 matrix:
   exclude:
-    - elixir: 1.8
-      otp_release: 21.0
     - elixir: 1.8
       otp_release: 20.3
     - elixir: 1.8
@@ -21,12 +19,12 @@ matrix:
       otp_release: 20.3
     - elixir: 1.7
       otp_release: 20.2
+    - elixir: 1.6
+      otp_release: 21.3
     - elixir: 1.6
       otp_release: 21.2
     - elixir: 1.6
       otp_release: 21.1
-    - elixir: 1.6
-      otp_release: 21.0
 services:
   - redis-server
 script: