Fix pg test and use default parameters in Result object

lib/Result.js

@@ -16,9 +16,9 @@ class Result {
 	 * @param {Array} [rows] - the data rows of the result
 	 * @param {Array} [columns] - the column names in the result
 	 */
-	constructor (rows, columns) {
-		this._rows = (rows == null) ? [] : rows;
-		this._columns = (columns == null) ? [] : columns;
+	constructor (rows=[], columns=[]) {
+		this._rows = rows;
+		this._columns = columns;
 
 		// If columns aren't explicitly given,
 		// get the list from the first row's keys

lib/adapters/Pg/index.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const Pg = require('./pg');
+const Pg = require('./Pg');
 
 module.exports = config => {
 	return new Pg(config.connection);