Simplify Gradle asciidoctor config

Author: marcphilipp

documentation/documentation.gradle

@@ -102,23 +102,23 @@ asciidoctor {
 
 	backends 'html5'
 
-	attributes	'jupiter-version': project.property('version'),
-				'platform-version': project.property('platformVersion'),
-				'vintage-version': project.property('vintageVersion'),
-				'bom-version': project.property('version'),
-				'junit4-version': project.property('junit4Version'),
-				'apiguardian-version': project.property('apiGuardianVersion'),
-				'ota4j-version': project.property('ota4jVersion'),
-				'release-branch': project.property('releaseBranch'),
-				'docs-version': project.property('docsVersion'),
-				'revnumber' : project.version,
-				'mainDir': project.sourceSets.main.java.srcDirs[0],
-				'testDir': project.sourceSets.test.java.srcDirs[0],
-				'kotlinTestDir': project.sourceSets.test.kotlin.srcDirs[0],
+	attributes	'jupiter-version': version,
+				'platform-version': platformVersion,
+				'vintage-version': vintageVersion,
+				'bom-version': version,
+				'junit4-version': junit4Version,
+				'apiguardian-version': apiGuardianVersion,
+				'ota4j-version': ota4jVersion,
 				'surefire-version': surefireVersion,
+				'release-branch': releaseBranch,
+				'docs-version': docsVersion,
+				'revnumber' : version,
+				'releaseBranch' : version,
+				'testDir': sourceSets.test.java.srcDirs[0],
+				'kotlinTestDir': sourceSets.test.kotlin.srcDirs[0],
 				'consoleLauncherOptionsFile': consoleLauncherOptionsFile.toString(),
 				'experimentalApisTableFile': experimentalApisTableFile.toString(),
-				'testResourcesDir': project.sourceSets.test.resources.srcDirs[0],
+				'testResourcesDir': sourceSets.test.resources.srcDirs[0],
 				'outdir': outputDir.absolutePath,
 				'source-highlighter': 'coderay@', // TODO switch to 'rouge' once supported by the html5 backend and on MS Windows
 				'tabsize': '4',