Fix postgres dependency

I was getting this error when starting a new project with +postgres
```
(Could not find artifact postgresql:postgresql:jar:9.3-1102-jdbc41 in central (http://repo1.maven.org/maven2/))
(Could not find artifact postgresql:postgresql:jar:9.3-1102-jdbc41 in clojars (https://clojars.org/repo/))
```

When the postgres dependency was updated from 9.1-901-1.jdbc4 to 9.3-1102-jdbc41 the group id also needed to be changed to org.postgresql

See http://search.maven.org/#artifactdetails%7Cpostgresql%7Cpostgresql%7C9.1-901-1.jdbc4%7Cjar
vs http://search.maven.org/#artifactdetails%7Corg.postgresql%7Cpostgresql%7C9.3-1102-jdbc41%7Cjar