Add Neo4j Maven repository

This resolves the build error

    > Could not find org.neo4j:neo4j-cypher-dsl:2.0.1.
      Required by:
          CityBikeDataExplorer:graph-db-driver:1.0 >
          org.springframework.data:spring-data-neo4j:3.0.1.RELEASE

Similar to http://stackoverflow.com/q/16653128