Fix invalid metadata: add `ignore` to bower.json

Bower complains about a non-existent `ignore` parameter in the `bower.json`
configuration. Added an empty array for now, but it seems like eventually it
might be better to ignore the example HTML files in the Github repo.
Merge pull request #114 from geoffharcourt/geoffharcourt-fix-bower-metadata

Fix invalid metadata: add `ignore` to bower.json