[TAP] Fix the XML serialization for 'foreignKey' items in /tables.

The order of its children was incorrect according to the XSD schema:
the 'fkColumn' must be written before 'description' and 'utype'.

src/tap/metadata/TAPMetadata.java

@@ -76,7 +76,7 @@ import uws.UWSToolBox;
  * </p>
  *
  * @author Gr&eacute;gory Mantelet (CDS;ARI)
- * @version 2.1 (09/2017)
+ * @version 2.1 (11/2017)
  */
 public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResource {
 
@@ -850,13 +850,13 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 	 * <pre>
 	 * &lt;foreignKey&gt;
 	 * 	&lt;targetTable&gt;...&lt;/targetTable&gt;
-	 * 	&lt;description&gt;...&lt;/description&gt;
-	 * 	&lt;utype&gt;...&lt;/utype&gt;
 	 * 	&lt;fkColumn&gt;
 	 * 		&lt;fromColumn&gt;...&lt;/fromColumn&gt;
 	 * 		&lt;targetColumn&gt;...&lt;/targetColumn&gt;
 	 * 	&lt;/fkColumn&gt;
 	 * 	...
+	 * 	&lt;description&gt;...&lt;/description&gt;
+	 * 	&lt;utype&gt;...&lt;/utype&gt;
 	 * &lt;/foreignKey&gt;
 	 * </pre>
 	 *
@@ -873,8 +873,6 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 		writer.println("\t\t\t<foreignKey>");
 
 		writeAtt(prefix, "targetTable", fk.getTargetTable().getRawName(), false, writer);
-		writeAtt(prefix, "description", fk.getDescription(), true, writer);
-		writeAtt(prefix, "utype", fk.getUtype(), true, writer);
 
 		final String prefix2 = prefix + "\t";
 		for(Map.Entry<String,String> entry : fk){
@@ -886,6 +884,9 @@ public class TAPMetadata implements Iterable<TAPSchema>, VOSIResource, TAPResour
 			writer.println("</fkColumn>");
 		}
 
+		writeAtt(prefix, "description", fk.getDescription(), true, writer);
+		writeAtt(prefix, "utype", fk.getUtype(), true, writer);
+
 		writer.println("\t\t\t</foreignKey>");
 	}