added import SimpleNamespace to DOAP.java

added import `import org.eclipse.rdf4j.model.impl.SimpleNamespace` to `DOAP.java`, as requested

Author: seralf

core/model/src/main/java/org/eclipse/rdf4j/model/vocabulary/DOAP.java

@@ -8,7 +8,9 @@
 package org.eclipse.rdf4j.model.vocabulary;
 
 import org.eclipse.rdf4j.model.IRI;
+import org.eclipse.rdf4j.model.Namespace;
 import org.eclipse.rdf4j.model.ValueFactory;
+import org.eclipse.rdf4j.model.impl.SimpleNamespace;
 import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
 
 /**