Update docker-library

- `buildpack-deps`: add `micro` variant without development headers
- `node`: NPM 2.1.9
- `php`: `zend_extension` loading in `docker-php-ext-install`, especially for `opcache`
- `sentry`: just `REAMDE.md` stub - figured I'd just update to get it out of the way :)
- `tomcat`: 6.0.43
- `wordpress`: 4.0.1