Merge pull request #644 from tuncer/travis-otp-20.0.4

travis-ci: otp 20.0.2 -> 20.0.4
diff --git a/.travis.yml b/.travis.yml
index 7af5258..dcb6606 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,7 @@
   - 17.0
   - 18.0
   - 19.1
-  - 20.0.2
+  - 20.0.4
 before_script:
   - hostname -f
   - cc -v