Use List instead of ArrayList where possible

Author: cmaglie

arduino-core/src/cc/arduino/contributions/libraries/LibrariesIndexer.java

@@ -60,7 +60,7 @@ public class LibrariesIndexer {
   private LibrariesIndex index;
   private final LibraryList installedLibraries = new LibraryList();
   private final LibraryList installedLibrariesWithDuplicates = new LibraryList();
-  private ArrayList<File> librariesFolders;
+  private List<File> librariesFolders;
   private final File indexFile;
   private final File stagingFolder;
   private File sketchbookLibrariesFolder;
@@ -101,12 +101,12 @@ private void parseIndex(File file) throws IOException {
     }
   }
 
-  public void setLibrariesFolders(ArrayList<File> _librariesFolders) {
+  public void setLibrariesFolders(List<File> _librariesFolders) {
     librariesFolders = _librariesFolders;
     rescanLibraries();
   }
 
-  public ArrayList<File> getLibrariesFolders() {
+  public List<File> getLibrariesFolders() {
     return librariesFolders;
   }