Update GEXF namespace url

modules/ExportPlugin/src/main/java/org/gephi/io/exporter/plugin/ExporterGEXF.java

@@ -92,22 +92,18 @@ public class ExporterGEXF implements GraphExporter, CharacterExporter, LongTask
 
     //GEXF
     private static final String GEXF = "gexf";
-    private static final String GEXF_NAMESPACE = "http://www.gexf.net/1.3";
-    private static final String GEXF_NAMESPACE_LOCATION = "http://www.gexf.net/1.3 http://www.gexf.net/1.3/gexf.xsd";
+    private static final String GEXF_NAMESPACE = "http://gexf.net/1.3";
+    private static final String GEXF_NAMESPACE_LOCATION = "http://gexf.net/1.3 http://gexf.net/1.3/gexf.xsd";
     private static final String VIZ = "viz";
-    private static final String VIZ_NAMESPACE = "http://www.gexf.net/1.3/viz";
+    private static final String VIZ_NAMESPACE = "http://gexf.net/1.3/viz";
     private static final String GEXF_VERSION = "version";
     private static final String GRAPH = "graph";
     private static final String GRAPH_MODE = "mode";
     private static final String GRAPH_DEFAULT_EDGETYPE = "defaultedgetype";
-    private static final String GRAPH_START = "start";
-    private static final String GRAPH_END = "end";
     private static final String GRAPH_TIMEFORMAT = "timeformat";
     private static final String GRAPH_TIMEREPRESENTATION = "timerepresentation";
     private static final String GRAPH_IDTYPE = "idtype";
     private static final String TIMESTAMP = "timestamp";
-    private static final String TIMESTAMPS = "timestamps";
-    private static final String INTERVALS = "intervals";
     private static final String META = "meta";
     private static final String META_LASTMODIFIEDDATE = "lastmodifieddate";
     private static final String META_CREATOR = "creator";