use \n instead of system "newline" property

src/net/java/sip/communicator/impl/gui/main/message/ChatWritePanel.java

@@ -167,7 +167,7 @@ public void actionPerformed(ActionEvent e)
             String editorText = editorPane.getText();
             
             editorPane.setText(editorText.substring(0, caretPosition)
-                    + System.getProperty("line.separator")
+                    + "\n"
                     + editorText.substring(caretPosition));
             
             editorPane.setCaretPosition(caretPosition + 1);