Add multiple versions of erlang to travis.

.travis.yml

@@ -1,6 +1,20 @@
 language: erlang
 
 otp_release:
+   - 18.0
+   - 17.5
+   - 17.4
+   - 17.3
    - 17.1
+   - 17.0
+   - R16B03-1
+   - R16B03
+   - R16B02
+   - R16B01
+   - R16B
+   - R15B03-1
+   - R15B02
+   - R15B01
+   - R15B
 
 script: "make travis"