Disable OpenJDK 13 travis job

Clashsoft · Clashsoft · commit d3b99538eecd · 2019-12-24T12:40:18.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -8,7 +8,8 @@ jdk:
   # - openjdk6  # minimum
   - openjdk8  # LTS
   - openjdk11 # LTS
-  - openjdk13 # latest
+  # disabled because the maven compiler for JDK 13 no longer supports source/target compatibility 6
+  # - openjdk13 # latest
 
 # required for UI tests
 services:
