added timestamp to log file

app/src/main/java/com/vsoft/vera/ui/ChatActivity.java

@@ -612,7 +612,8 @@ public class ChatActivity extends AppCompatActivity implements OnDSListener, OnD
 
     private void exportAndSaveLogs(List<ChatLog> chatLogList) {
         String baseDir = android.os.Environment.getExternalStorageDirectory().getAbsolutePath();
-        String fileName = "chatlog.csv";
+        String dateString = Util.getDateTime(new Date().getTime());
+        String fileName = "ChatLogs_" + dateString + ".csv";
         String filePath = baseDir + File.separator + fileName;
         File f = new File(filePath);
         CSVWriter writer;