Asciidoctor: Do not copy target/** to aj-build/dist

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

docs/pom.xml

                         <exclude>developer/traces/**</exclude>
                         <exclude>install/**</exclude>
                         <exclude>sandbox/**</exclude>
+                        <exclude>target/**</exclude>
                         <exclude>teaching/**</exclude>
                         <exclude>test/**</exclude>
                       </excludes>