Allow Missing META.json Field if it was not required at time of Release

[theory]

When reindexing stuff, I saw a bunch of errors like this:

The italian_fts-1.2.0/META.json file does not adhere to the <a href="http://pgxn.org/spec/">PGXN Meta Specification</a>. Errors:<br/>• Required field /provides: missing [Spec v1.0.0]

It's possible, perhaps likely, that this release and others with this error pre-date the time when /provides was required. Ideally PGXN::Meta::Validator and the related code in the database functions would know this and check the requirements related to the version listed in the META.json file, but it may be that they didn't specify that it was a prerelease version of the spec (the requirement was added in PGXN::Meta::Validator on 2011-06-01T03:51:17 and the spec was updated to v1.0.0 on 0.14.0 2012-01-10T04:10:22Z), so maybe compare the date when reindexing.