Use unique function

Author: jfmengels

lib/elm-files.js

@@ -53,9 +53,9 @@ async function getProjectFiles(options, elmSyntaxVersion) {
   const emptyDirectories = filesInDirectories.filter(
     ({files}) => files.length === 0
   );
-  const elmFilesToRead = [
-    ...new Set(filesInDirectories.flatMap((directory) => directory.files))
-  ];
+  const elmFilesToRead = unique(
+    filesInDirectories.flatMap((directory) => directory.files)
+  );
 
   // TODO(@jfmengels): Have a different message depending on how directories were chosen (CLI directories, application, package).
   if (options.directoriesToAnalyze.length > 0 && emptyDirectories.length > 0) {