Added build-configuration to java7 in pom-file, otherwise it will not bu...

Couldn't build with: 
        Apache Maven 3.0.4
        Maven home: /usr/share/maven
        Java version: 1.7.0_55, vendor: Oracle Corporation
        Java home: /usr/lib/jvm/java-7-oracle/jre
        Default locale: en_US, platform encoding: UTF-8
        OS name: "linux", version: "3.8.0-35-generic", arch: "amd64", family: "unix

Change in build-target and source in pom.xml worked out just fine.