fix META.yml syntax

Bah, used lists where simple maps were expected (though this syntax is
used with optional_features and another project of mine, so slightly
excusable except for missing tests).

Also, Test::YAML::Meta wants keys of optional_features to conform to
/^[a-z_-]+$/.  This isn't mentioned anywhere in the specifications, but
a passing test is more useful than a minor stylistic detail.

Finally, while 'repository' apparantly still isn't an official resources
key, it _is_ mentioned as such (lowercased) in the specs.  In fact
everyone seems to use it like that, so I guess being technically
incorrect will be supported better.