replace deprecated constant FileFileFilter.FILE in javadoc (#657)

Author: orthlus

src/main/java/org/apache/commons/io/FileUtils.java

@@ -584,7 +584,7 @@ public static void copyDirectory(final File srcDir, final File destDir, final bo
      * <pre>
      * // Create a filter for ".txt" files
      * IOFileFilter txtSuffixFilter = FileFilterUtils.suffixFileFilter(".txt");
-     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.FILE, txtSuffixFilter);
+     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.INSTANCE, txtSuffixFilter);
      *
      * // Create a filter for either directories or ".txt" files
      * FileFilter filter = FileFilterUtils.orFileFilter(DirectoryFileFilter.DIRECTORY, txtFiles);
@@ -635,7 +635,7 @@ public static void copyDirectory(final File srcDir, final File destDir, final Fi
      * <pre>
      * // Create a filter for ".txt" files
      * IOFileFilter txtSuffixFilter = FileFilterUtils.suffixFileFilter(".txt");
-     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.FILE, txtSuffixFilter);
+     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.INSTANCE, txtSuffixFilter);
      *
      * // Create a filter for either directories or ".txt" files
      * FileFilter filter = FileFilterUtils.orFileFilter(DirectoryFileFilter.DIRECTORY, txtFiles);
@@ -686,7 +686,7 @@ public static void copyDirectory(final File srcDir, final File destDir, final Fi
      * <pre>
      * // Create a filter for ".txt" files
      * IOFileFilter txtSuffixFilter = FileFilterUtils.suffixFileFilter(".txt");
-     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.FILE, txtSuffixFilter);
+     * IOFileFilter txtFiles = FileFilterUtils.andFileFilter(FileFileFilter.INSTANCE, txtSuffixFilter);
      *
      * // Create a filter for either directories or ".txt" files
      * FileFilter filter = FileFilterUtils.orFileFilter(DirectoryFileFilter.DIRECTORY, txtFiles);