Fix vesion update for beta 1 to beta 2

WHoops! Reviewed by Jelle ;)

plugins/VersionUpgrade/VersionUpgrade49to50/__init__.py

@@ -17,6 +17,8 @@ def getMetaData() -> Dict[str, Any]:
             ("preferences", 6000016):        ("preferences", 6000018,        upgrade.upgradePreferences),
             ("machine_stack", 5000016):      ("machine_stack", 5000018,      upgrade.upgradeStack),
             ("extruder_train", 5000016):     ("extruder_train", 5000018,     upgrade.upgradeStack),
+            ("machine_stack", 4000018):      ("machine_stack", 5000018,      upgrade.upgradeStack),  # We made a mistake in the arachne beta 1
+            ("extruder_train", 4000018):     ("extruder_train", 5000018,     upgrade.upgradeStack),  # We made a mistake in the arachne beta 1
             ("definition_changes", 4000016): ("definition_changes", 4000018, upgrade.upgradeInstanceContainer),
             ("quality_changes", 4000016):    ("quality_changes", 4000018,    upgrade.upgradeInstanceContainer),
             ("quality", 4000016):            ("quality", 4000018,            upgrade.upgradeInstanceContainer),