feat: use @xen-orchestra/cron (#2619)

Fixes #2616

packages/xo-server/package.json

@@ -34,6 +34,7 @@
   "dependencies": {
     "@marsaud/smb2-promise": "^0.2.1",
     "@nraynaud/struct-fu": "^1.0.1",
+    "@xen-orchestra/cron": "^1.0.0",
     "ajv": "^6.1.1",
     "app-conf": "^0.5.0",
     "archiver": "^2.1.0",
@@ -46,7 +47,6 @@
     "connect-flash": "^0.1.1",
     "cookie": "^0.3.1",
     "cookie-parser": "^1.4.3",
-    "cron": "^1.3.0",
     "d3-time-format": "^2.1.1",
     "debug": "^3.1.0",
     "decorator-synchronized": "^0.3.0",