test only 18.0 and later

.travis.yml

@@ -1,12 +1,13 @@
 language: erlang
 script: "GPROC_DIST=true rebar get-deps compile eunit"
 otp_release:
-    - 17.1
-    - 17.0
-    - R16B03-1
-    - R16B02
-    - R16B01
-    - R16B
-    - R15B03
-    - R15B02
-    - R15B01
+    - 20.0
+    - 19.3
+    - 19.2
+    - 19.1
+    - 19.0
+    - 18.3
+    - 18.2.1
+    - 18.2
+    - 18.1
+    - 18.0