Travis: Replace Oracle JDK 10 with Open JDK 10, because Oracle JKD 10 is no longer available on travis.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/codec/trunk@1844395 13f79535-47bb-0310-9956-ffa450edef68

Author: PascalSchumacher

.travis.yml

@@ -20,7 +20,7 @@ jdk:
   - openjdk7
   - oraclejdk8
   - oraclejdk9
-  - oraclejdk10
+  - openjdk10
 
 script:
   - mvn