Fix memory leak (metafacture-core#666)

Let maps implement Closeable.
Bump metafacture-core version.

Author: dr0i

build.gradle

@@ -44,7 +44,7 @@ subprojects {
       'jquery':         '3.3.1-1',
       'junit_jupiter':  '5.8.2',
       'junit_platform': '1.4.2',
-      'metafacture':    '5.7.0',
+      'metafacture':    '5.7.1',
       'mockito':        '2.27.0',
       'requirejs':      '2.3.6',
       'slf4j':          '1.7.21',
@@ -54,7 +54,7 @@ subprojects {
   }
 
   group = 'org.metafacture'
-  version = '0.8.0-SNAPSHOT'
+  version = '0.7.1'
 
   apply plugin: 'checkstyle'
   apply plugin: 'eclipse'
@@ -72,6 +72,7 @@ subprojects {
   repositories {
     mavenCentral()
     maven githubPackage.invoke("metafacture")
+    mavenLocal()
   }
 
   dependencies {

metafix/src/main/java/org/metafacture/metafix/maps/RdfMap.java

@@ -31,6 +31,7 @@
 import org.apache.jena.riot.RDFDataMgr;
 import org.apache.jena.shared.PropertyNotFoundException;
 
+import java.io.Closeable;
 import java.io.IOException;
 import java.net.HttpURLConnection;
 import java.net.URL;
@@ -56,7 +57,7 @@
  *
  * @see org.metafacture.metamorph.maps.FileMap
  */
-public final class RdfMap extends AbstractReadOnlyMap<String, String> {
+public final class RdfMap extends AbstractReadOnlyMap<String, String> implements Closeable {
 
     public static final String SELECT = "select";
     public static final String TARGET = "target";
@@ -394,6 +395,14 @@ private String read(final String url) throws IOException {
         return conn.getURL().toString();
     }
 
+    @Override
+    public void close() {
+        map.clear();
+        if (model != null) {
+            model.close();
+        }
+    }
+
     private enum Select {
         SUBJECT, OBJECT, DEFAULT
     }