What is your PHP version?
I have marked the issue fixed because the use of the static keyword at that location is unnecessary and could be replaced with self. However, static is still perfectly valid there in current versions of PHP, so my question is still relevant.
You will be unable to install or upgrade VaultWiki 4 if your PHP version is less than 5.3. The installer uses a variant of anonymous functions that was not introduced until 5.3.