Missing builtins / old pg-types reference

[vitaly-t]

According to this, we have access to types.builtins from the pg driver, in the following manner:

const types = require('pg').types;
const someType = types.builtins.TIMESTAMPTZ;

In reality, however, pg.types does not have property builtins, because pg-types implemented it with version 2.1.0, but we include it as ~ instead of ^ like everything else.

And so there is discrepancy between the official documentation and reality.

[vitaly-t]

I have added PR that fixes that.