Just support current version minus two

Author: devinus

.travis.yml

@@ -3,32 +3,9 @@ elixir:
   - 1.7.0
   - 1.6.6
   - 1.6.5
-  - 1.6.4
-  - 1.6.3
-  - 1.6.2
-  - 1.6.1
-  - 1.6.0
 otp_release:
   - 21.0
   - 20.3
   - 20.1
   - 20.0
-matrix:
-  exclude:
-    - elixir: 1.7.0
-      opt_release: 20.3
-    - elixir: 1.7.0
-      opt_release: 20.1
-    - elixir: 1.7.0
-      opt_release: 20.0
-    - elixir: 1.6.4
-      opt_release: 21.0
-    - elixir: 1.6.3
-      opt_release: 21.0
-    - elixir: 1.6.2
-      opt_release: 21.0
-    - elixir: 1.6.1
-      opt_release: 21.0
-    - elixir: 1.6.0
-      opt_release: 21.0
 sudo: false