fix: Relax Allow Header Test (#562)

Problem: The test asserted the order of methods in the Allow header. The
order is irrelevant for the header and not guaranteed by the code, so
that the test failed using Node 10.

Solution: Adjust the assertion to check the returned methods
irrespective of order.

test/allow.header.spec.ts

@@ -18,12 +18,15 @@ describe(packageJson.name, () => {
     app.server.close();
   });
 
-  it('adds allow header to 405 - Method Not Allowed', async () =>
+  it('adds "Allow" header to 405 - Method Not Allowed', async () =>
     request(app)
       .put('/v1/pets/greebo')
       .expect(405)
       .then((response) => {
-        expect(response.header).to.include({ allow: 'POST, GET' });
+        expect(response.header.allow.split(', ')).to.have.members([
+          'GET',
+          'POST',
+        ]);
       }));
 });