fix docs (#135)

* fix docs

* Update index.asciidoc

docs/index.asciidoc

@@ -43,7 +43,7 @@ A `[geoip][location]` field is created if
 the GeoIP lookup returns a latitude and longitude. The field is stored in
 http://geojson.org/geojson-spec.html[GeoJSON] format. Additionally,
 the default Elasticsearch template provided with the
-<<plugins-outputs-elasticsearch,`elasticsearch` output>> maps
+{logstash-ref}/plugins-outputs-elasticsearch.html[elasticsearch output] maps
 the `[geoip][location]` field to an http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-geo-point-type.html#_mapping_options[Elasticsearch geo_point].
 
 As this field is a `geo_point` _and_ it is still valid GeoJSON, you get