backend-pg: bump "pg" to latest version

Trying to fix:

    TypeError: Cannot call method 'sync' of undefined
      at Query.handleError (/voxer/deploy/server/node_modules/zag-backend-pg/node_modules/pg/lib/query.js:92:16)
      at Client.connect (/voxer/deploy/server/node_modules/zag-backend-pg/node_modules/pg/lib/client.js:184:24)
      at g (events.js:192:14)
      at EventEmitter.emit (events.js:93:17)
      at Socket.<anonymous> (/voxer/deploy/server/node_modules/zag-backend-pg/node_modules/pg/lib/connection.js:60:10)
      at Socket.EventEmitter.emit (events.js:93:17)
      at TCP.onread (net.js:423:51)

via https://github.com/brianc/node-postgres/pull/572.
backend-pg: v0.0.4