fix: addPbxGroup nested folders with relative path

Author: KristianDD

lib/pbxProject.js

@@ -555,15 +555,16 @@ pbxProject.prototype.addPbxGroup = function (filePathsArray, name, path, sourceT
         }
 
         var srcRootPath = $path.dirname($path.dirname(this.filepath));
-        var file = new pbxFile($path.relative(srcRootPath, filePath));
+        var relativePath = $path.relative(srcRootPath, filePath);
+        var file = new pbxFile(opt.filesRelativeToProject ? relativePath : filePath);
         if (fs.existsSync(filePath) && fs.lstatSync(filePath).isDirectory()) {
             file.uuid = this.generateUuid();
             file.fileRef = file.uuid;
             this.addToPbxFileReferenceSection(file);    // PBXFileReference
             this.addToPbxBuildFileSection(file);
             pbxGroup.children.push(pbxGroupChild(file));
             var files = fs.readdirSync(filePath).map(p => $path.join(filePath, p));
-            this.addPbxGroup(files, $path.basename(filePath), filePath, null, {uuid: file.uuid});
+            this.addPbxGroup(files, $path.basename(filePath), filePath, null, {uuid: file.uuid, filesRelativeToProject: opt.filesRelativeToProject});
         } else if (isSourceOrHeaderFileType(file.lastKnownFileType)) {
             file.uuid = this.generateUuid();
             file.fileRef = this.generateUuid();