Fix postgres ssl connection options

[addnab]

SSL connection options aren't passed through to the pg.Client if config.connectionString is present.

Example:-
If Postgrator is initialized like so

const postgrator = new Postgrator({
  driver: 'pg',
  migrationDirectory: `...`,
  connectionString: "postgres://...",
  ssl: {
    rejectUnauthorized: false
  }
});

then the pg.Client is not initialized with the ssl options.

Since config.connectionString is accepted by pg.Client, this change should be backward compatible.

[addnab]

@rickbergfalk Can you review and publish this please?

[rickbergfalk]

Sorry I missed this @addnab will publish shortly