Use latest minor erlang releases for travis builds

.travis.yml

@@ -10,10 +10,10 @@ install: "true"
 language: erlang
 otp_release:
   - 21.0
-  - 20.0
-  - 19.1
+  - 20.3
+  - 19.3
   - 18.3
-  - 17.4
+  - 17.5
   - R16B03-1
 script:
   - make elvis