Change pom.xml for OpenJDK8

[alawvt]

Because of the change in the Oracle Java license, we installed OpenJDK8. To work, we had to change pom.xml to

<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
</plugin>