Use ObjectFactory.directoryProperty() if possible

ProjectLayout.directoryProperty() was deprecated in Gradle 5.0 and
replaced with ObjectFactory.directoryProperty(). In order to stay
backward compatible with Gradle 4.x, the latter is now called first and
the former is used as a fallback.

Resolves ajoberstar#64.

src/main/java/org/ajoberstar/gradle/git/publish/GitPublishExtension.java

@@ -1,6 +1,7 @@
 package org.ajoberstar.gradle.git.publish;
 
 
+import org.ajoberstar.gradle.git.publish.tasks.DirectoryPropertyFactory;
 import org.gradle.api.Action;
 import org.gradle.api.Project;
 import org.gradle.api.file.CopySpec;
@@ -18,7 +19,7 @@ public class GitPublishExtension {
   private final PatternFilterable preserve;
 
   public GitPublishExtension(Project project) {
-    this.repoDir = project.getLayout().directoryProperty();
+    this.repoDir = DirectoryPropertyFactory.create(project);
     this.repoUri = project.getObjects().property(String.class);
     this.branch = project.getObjects().property(String.class);
     this.commitMessage = project.getObjects().property(String.class);

src/main/java/org/ajoberstar/gradle/git/publish/tasks/DirectoryPropertyFactory.java

@@ -0,0 +1,28 @@
+package org.ajoberstar.gradle.git.publish.tasks;
+
+import org.gradle.api.Project;
+import org.gradle.api.file.DirectoryProperty;
+import org.gradle.api.file.ProjectLayout;
+import org.gradle.api.model.ObjectFactory;
+
+/**
+ * For backward compatibility with Gradle 4.x
+ */
+public class DirectoryPropertyFactory {
+
+    private DirectoryPropertyFactory() {
+    }
+
+    public static DirectoryProperty create(Project project) {
+        return create(project.getLayout(), project.getObjects());
+    }
+
+    public static DirectoryProperty create(ProjectLayout layout, ObjectFactory objectFactory) {
+        try {
+            return objectFactory.directoryProperty();
+        } catch (NoSuchMethodError e) {
+            return layout.directoryProperty();
+        }
+    }
+
+}

src/main/java/org/ajoberstar/gradle/git/publish/tasks/GitPublishReset.java

@@ -39,7 +39,7 @@ public class GitPublishReset extends DefaultTask {
   @Inject
   public GitPublishReset(ProjectLayout layout, ObjectFactory objectFactory) {
     this.grgit = objectFactory.property(Grgit.class);
-    this.repoDirectory = layout.directoryProperty();
+    this.repoDirectory = DirectoryPropertyFactory.create(layout, objectFactory);
     this.repoUri = objectFactory.property(String.class);
     this.branch = objectFactory.property(String.class);