test(rxForm): Dropdown page object

It did on my machine. Why wouldn't it?

```
15:14:59 (e2e-rx-form-generic-helpers) ~/code/js/encore-ui
$: ./node_modules/protractor/bin/protractor protractor.conf.js --specs=src/rxForm/docs/rxForm.midway.js 
Using the selenium server at http://localhost:4444/wd/hub


  rxForm
    ✓ should have the right number of options 
    ✓ should have every option listed (4877ms)
    ✓ should have a selected option by default 
    ✓ should not select another option 
    ✓ should report non-existing options 
    ✓ should report existing options 
    ✓ should select a new option 
    ✓ should have a value 


  8 passing (9s)

```