Consider passing the YAML SyntaxError to the fore

Instead of swallowing `SyntaxError` and indicating a generic error message, consider passing the syntax error message with the location so that the user can focus on fixing the error.

https://github.com/travis-ci/travis-lint/blob/095fd80b2f8bae5aee261fa290de8bf2d5135041/lib/travis/lint/runner.rb#L62-L63