Create enumerable properties for properties.path()

The return value of properties.path() had enumerable keys in 2.1.1 and
earlier. Starting in 2.2.0, the keys were no longer enumerable as part
of the change made for steveukx#40 in 0877cc8.

Fixes steveukx#58

src/properties-reader.js

@@ -217,14 +217,14 @@ PropertiesReader.prototype.set = function (key, value) {
       }
 
       if (!has(source, step)) {
-         Object.defineProperty(source, step, { value: {} });
+         Object.defineProperty(source, step, { value: {}, enumerable: true });
       }
 
       source = source[step]
    }
 
    if (expanded[0] === '__proto__') {
-      Object.defineProperty(source, expanded[0], { value: parsedValue });
+      Object.defineProperty(source, expanded[0], { value: parsedValue, enumerable: true });
    }
    else if (typeof parsedValue === 'string' && typeof  source[expanded[0]] === 'object') {
       source[expanded[0]][''] = parsedValue;

test/reader.spec.js

@@ -105,6 +105,13 @@ describe('Reader', () => {
       expect(properties.path().foo.bar).toBe('A Value');
    });
 
+   it('Property paths are enumerable', async () => {
+      await givenTheProperties('some.property=Value');
+
+      expect(Object.keys(properties.path())).toEqual(['some']);
+      expect(Object.keys(properties.path().some)).toEqual(['property']);
+   });
+
    it('Sets properties into an app', async () => {
       const set = jest.fn();
       (await givenTheProperties(`