Fix java 6 build on travis:

- install open-jdk6, as it was removed from the default travis image
- install a java 6 compatible maven version 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/codec/trunk@1809449 13f79535-47bb-0310-9956-ffa450edef68

Author: PascalSchumacher

.travis.yml

@@ -21,5 +21,17 @@ jdk:
   - openjdk7
   - oraclejdk8
 
+addons:
+  apt:
+    packages:
+      - openjdk-6-jdk
+
+# use java 6 compatible maven version (installed into target directory so rat check passes)
+before_install:
+  - wget https://archive.apache.org/dist/maven/maven-3/3.2.5/binaries/apache-maven-3.2.5-bin.zip -P ./target
+  - unzip -qq ./target/apache-maven-3.2.5-bin.zip -d ./target
+  - export M2_HOME=$PWD/target/apache-maven-3.2.5
+  - export PATH=$M2_HOME/bin:$PATH
+
 after_success:
   - mvn clean cobertura:cobertura coveralls:report