[CSV-239] Cannot get headers in column order from CSVRecord.

Undo previous change.

Author: Gary Gregory

src/main/java/org/apache/commons/csv/CSVParser.java

@@ -35,6 +35,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -441,7 +442,7 @@ public void close() throws IOException {
     private Map<String, Integer> createEmptyHeaderMap() {
         return this.format.getIgnoreHeaderCase() ?
                 new TreeMap<>(String.CASE_INSENSITIVE_ORDER) :
-                new TreeMap<>();
+                new LinkedHashMap<>();
     }
 
     /**