fix(postgres-driver): Clean-up deprecation warning (#531)

Author: jcw-

packages/cubejs-postgres-driver/driver/PostgresDriver.js

@@ -32,7 +32,7 @@ class PostgresDriver extends BaseDriver {
       port: process.env.CUBEJS_DB_PORT,
       user: process.env.CUBEJS_DB_USER,
       password: process.env.CUBEJS_DB_PASS,
-      ssl: (process.env.CUBEJS_DB_SSL || 'false').toLowerCase() === 'true' ? {} : undefined,
+      ssl: (process.env.CUBEJS_DB_SSL || 'false').toLowerCase() === 'true' ? { rejectUnauthorized: true } : undefined,
       ...config
     });
     this.pool.on('error', (err) => {