Fix 2 internal doc links (#1837)

Signed-off-by: Arend von Reinersdorff <[email protected]>

src/main/asciidoc/inc/_registry.adoc

@@ -10,7 +10,7 @@ registry. This registry (or the default `docker.io` if no
 registry is given) is used during push and pull operations. This
 plugin follows the same semantics, so if an image name is specified
 with a registry part, this registry is contacted. Authentication is
-explained in the next <<_authentication,section>>.
+explained in the next <<authentication,section>>.
 
 There are some situations however where you want to have more
 flexibility for specifying a remote registry. This might be because

src/main/asciidoc/inc/external/_property_configuration.adoc

@@ -281,7 +281,7 @@ See <<list-properties>>.
 | specifies a path to a port mapping used when starting a container.
 
 | *docker.ports.idx*
-| Sets a port mapping. For example `<docker.ports.1>jolokia.ports:8080<docker.ports.1>` maps the container port 8080 dynamically to a host port and assigns this host port to the Maven property `${jolokia.port}`. See <<_port-mapping,Port mapping>> for possible mapping options. When creating images images only the right most port is used for exposing the port. For providing multiple port mappings, the index should be count up.
+| Sets a port mapping. For example `<docker.ports.1>jolokia.ports:8080<docker.ports.1>` maps the container port 8080 dynamically to a host port and assigns this host port to the Maven property `${jolokia.port}`. See <<start-port-mapping,Port mapping>> for possible mapping options. When creating images images only the right most port is used for exposing the port. For providing multiple port mappings, the index should be count up.
 See <<list-properties>> for more information about list properties.
 
 | *docker.registry*