Update docker-library images

- `node`: NPM 2.1.7
- `php`: cut image sizes roughly in half across the board (docker-library/php#36)
- `redis`: drop official support for versions upstream doesn't support (docker-library/redis#15)
- `wordpress`: fix `chown` issue (docker-library/wordpress#21)
Merge pull request #302 from infosiftr/update-docker-library

Update docker-library images