Added classifier for java 8 jars

[aegyed]

This way these could be deployed to maven central and be accessed with classifier java8.
(If you are willing to add an extra step to the pipeline...)

        <dependency>
            <groupId>se.digg.dgc</groupId>
            <artifactId>dgc-schema</artifactId>
            <version>${dgc-java.version}</version>
            <classifier>java8</classifier>
        </dependency>
        <dependency>
            <groupId>se.digg.dgc</groupId>
            <artifactId>dgc-create-validate</artifactId>
            <version>${dgc-java.version}</version>
            <classifier>java8</classifier>
        </dependency>

[martin-lindstrom]

@aegyed I actually tried just this, but for some reason the deploy doesn't work.