Update .travis.yml to match release versions used in main repo
diff --git a/.travis.yml b/.travis.yml
index fb55c70..d54ddc6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,9 +1,9 @@
 language: erlang
 
 otp_release:
-  - 18.1
-  - 18.0
-  - 17.5
+  - 21.1
+  - 20.3
+  - 19.3
 
 sudo: false