Hi the script is reporting as wrong because you never completed the 3.0.12 upgrade, or the version number would have been correct (maybe there was an error you missed back then). Anyway, if you click to ignore the script version and continue, it will upgrade successfully. If you're receiving that error on step 2, then you have skipped step 1 (at least since hitting upgrade.php or disabling VaultWiki manually), which enables the plugin that defines the missing function.
Also, 3.0.12 was a rushed release due to a security error. 3.0.13 is more stable as it simply fixes the bugs we didn't have time to fix in the previous version. There are no other changes in 3.0.13.