Bump versions in travis (#583)
Bump versions in travis (#583)

- WordPress 4.7 + 4.6
- PHP nightly + 7.0 + 5.6 + 5.2
GoogleForCreators/web-stories-wp,GoogleForCreators/web-stories-wp,GoogleForCreators/web-stories-wp,GoogleForCreators/web-stories-wp,GoogleForCreators/web-stories-wp