Fix test for successful invite

The message was updated in b91a58d, but the test was never updated to
reflect

test/index.js

@@ -46,7 +46,7 @@ describe('slackin', () => {
         .post('/invite')
         .send({ email: '[email protected]' })
         .expect('Content-Type', /json/)
-        .expect(200, { msg: 'success' })
+        .expect(200, { msg: 'WOOT. Check your email!' })
         .end(done);
     });