Update docker-library images

- `buildpack-deps`: added `curl` since we already had all the deps and it was a minuscule addition
- `gcc`: 4.9.2
- `java`: 7u71
- `mongo`: 2.7.8
- `node`: NPM 2.1.6 and Node 0.10.33
- `rails`: 4.1.7 and Ruby 2.1.4
- `wordpress`: `php:apache` is now the official base