Fixed java to openjdk6 due to bug https://bugs.eclipse.org/bugs/show_bug.cgi?id=412945

Author: gortazar

.travis.yml

@@ -1,4 +1,6 @@
 language: java
+jdk:
+  - openjdk6
 before_install: "cd es.sidelab.pascaline.parent"
 install: "mvn install"
 script: "mvn package"