Update .travis.yml
diff --git a/.travis.yml b/.travis.yml
index ab8409e..38347ca 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,6 @@
 
 os: linux
 otp_release:
-  - 21.0
   - 20.0
   - 19.3
   - 18.3