chore: incrementing version number - v1.15.3

(cherry picked from commit c0d406ae68c285da3ad6ce630e7e73d20f1a7a22)
Signed-off-by: Misty (Bot) <deploy@nodebb.org>

install/package.json

@@ -2,7 +2,7 @@
     "name": "nodebb",
     "license": "GPL-3.0",
     "description": "NodeBB Forum",
-    "version": "1.15.3-beta.0",
+    "version": "1.15.3",
     "homepage": "http://www.nodebb.org",
     "repository": {
         "type": "git",