Set minBoxVersion to 0.13.3 (smtp auth)

CloudronManifest.json

@@ -25,5 +25,6 @@
     "https://wordpress.org/about/shots/1.5/front-5.png",
     "https://wordpress.org/about/shots/1.5/front-3.png"
  ],
- "changelog": "file://CHANGELOG"
+ "changelog": "file://CHANGELOG",
+ "minBoxVersion": "0.13.3"
 }