switch node-postges library to a pure js implementation

I've updated package.json and all corresponding references as stated in https://github.com/brianc/node-postgres-pure usage guide. 
All tests ran fine (w/ 2 pending though):
```
$ npm test

> sails-postgresql@0.10.5 test /home/sdf/projects/sails-postgresql
> make test-integration

info: Testing `sails-postgresql`, a Sails/Waterline adapter.
info: Running `waterline-adapter-tests` against 4 interfaces...
info: ( semantic, queryable, migratable, associations )

debug: Latest draft of Waterline adapter interface spec:
debug: http://links.sailsjs.org/docs/plugins/adapters/interfaces

  216 passing (9s)
  2 pending
time elapsed: 9269ms
```