Solve issue #6. All data are stored in a file for each fold

src/main/java/be/cylab/java/wowa/training/Utils.java

@@ -472,7 +472,7 @@ final class Utils {
             final double wowa_accuracy,
             final double wowa_f_1) {
         try (OutputStreamWriter writer = new OutputStreamWriter(
-                new FileOutputStream(filename),
+                new FileOutputStream(filename, true),
                 StandardCharsets.UTF_8)) {
 
             writer.write("___________________________________________\n");
@@ -531,7 +531,7 @@ final class Utils {
             final double average_accuracy,
             final double average_f_1) {
         try (OutputStreamWriter writer = new OutputStreamWriter(
-                new FileOutputStream(filename),
+                new FileOutputStream(filename, true),
                 StandardCharsets.UTF_8)) {
 
             writer.write("___________________________________________\n");