Update the COLORPALETTE_DIR constant to point to new directory.

Related to the previous commit updating composer to install this in
the vendor directory but the caused the module to not find
the css/ColorPaletteField.css file.

_config.php

@@ -1,4 +1,4 @@
 <?php
 
 define('COLORPALETTE_PATH', __DIR__);
-define('COLORPALETTE_DIR', basename(__DIR__));
+define('COLORPALETTE_DIR', 'vendor/heyday/' .basename(__DIR__));