Only use double-quotes if necessary

We have super inconsistent usage of single and double quoted strings throughout both our Ruby and Javascript. This just deals with Ruby, but figured I'd point that out too.

This should make you cringe:
```ruby
it 'renders form errors' do
  expect(page).to have_css("#super-bad-errors")
end
```

I'm of the belief that you should use only use double quotes (`"`) if you need their functionality: string interpolation, using single-quotes, special characters.

It would be great to get the whole app to use one style or the other, so long as it's consistent.