Be more strict with the type of .arclint properties.

Summary: Although this provides less context in terms of the error message (for example, Parameter has invalid type. Expected type 'optional regex|list<regex>', got type 'list<string>'.), I think that it is the right approach. I think that PhutilTypeSpec::checkMap should be improved such that additional context is provided in the exception message.

Test Plan: Ran arc lint. Modified .arclint to contain an invalid regex and ran arc lint again.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9089