Fix package.json version to be 2.4 (#284)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "opensourcepos",
-  "version": "2.3.3",
+  "version": "2.4",
   "description": "Open Source Point of Sale is a web based point of sale system written in the PHP language. It uses MySQL as the data storage back-end and has a simple user interface.",
   "main": "index.php",
   "scripts": {