fix: Allow numbers and objects in filters

For example: `filter={["thing", "==", db.doc("things/" + thing)]}`

fix #16

README.md

@@ -206,6 +206,22 @@ Passing in an array of arrays creates a compound query to filter the collection
 />
 ```
 
+Passing in document references allows you to filter by reference fields:
+
+```jsx
+<FirestoreCollection
+  path={'users'}
+  filter={[
+    'organization',
+    '==',
+    firestore.collection('organizations').doc('foocorp'),
+  ]}
+  render={() => {
+    /* render stuff*/
+  }}
+/>
+```
+
 ##### render
 
 > function({}) | _required_

src/FirestoreCollection.js

@@ -8,7 +8,13 @@ class FirestoreCollection extends Component {
     sort: PropTypes.string,
     limit: PropTypes.number,
     filter: PropTypes.oneOfType([
-      PropTypes.arrayOf(PropTypes.string),
+      PropTypes.arrayOf(
+        PropTypes.oneOfType([
+          PropTypes.string,
+          PropTypes.number,
+          PropTypes.object,
+        ]),
+      ),
       PropTypes.arrayOf(PropTypes.array),
     ]),
     children: PropTypes.func,

src/__tests__/collection.filter.js

@@ -71,3 +71,25 @@ test('filters the documents returned with a compound filter', () => {
     }),
   );
 });
+
+test('filter accepts objects and numbers', () => {
+  const { firestoreMock } = createMocksForCollection();
+  const renderMock = jest.fn().mockReturnValue(<div />);
+  const collectionName = 'users';
+  mount(
+    <FirestoreCollection
+      path={collectionName}
+      filter={['number', '==', 5]}
+      render={renderMock}
+    />,
+    { context: { firestoreDatabase: firestoreMock, firestoreCache: {} } },
+  );
+  mount(
+    <FirestoreCollection
+      path={collectionName}
+      filter={['ref', '==', firestoreMock.doc('things/foobar')]}
+      render={renderMock}
+    />,
+    { context: { firestoreDatabase: firestoreMock, firestoreCache: {} } },
+  );
+});