Bumps pg version so node 14+ can be used

[bromeostasis]

Somewhat related to #28 , but I need to bump the pg version so I can run node 14+.

All tests are passing, though I wasn't able to verify anything more than that!

Relevant documentation: https://node-postgres.com/

At the time of this writing node-postgres is compatible with node 8.x, 10.x, 12.x and 14.x To use node >= 14.x you will need to install [email protected] or later due to some internal stream changes on the node 14 branch. Dropping support for an old node lts version will always be considered a breaking change in node-postgres and will be done on major version number changes only, and we will try to keep support for 8.x for as long as reasonably possible.