(fix): Failing spec under Rails 5
(fix): Failing spec under Rails 5

After installing Rails 5 and freshly installing this gem, the following spec fails:

```
1) FoundationRailsHelper::FormHelper input generators should generate datetime_field input
     Failure/Error: expect(node).to have_css('input[type="datetime"][name="author[forty_two]"]')
       expected #has_css?("input[type=\"datetime\"][name=\"author[forty_two]\"]") to return true, got false
```

It's failing because the `type` is now `datetime-local` (see below). [This has been introduced in Rails 5](http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-datetime_field)
([Old behaviour was to set type as `datetime`](http://api.rubyonrails.org/v4.2.0/classes/ActionView/Helpers/FormHelper.html#method-i-datetime_field))

Here's what the capybara node looks like:
```
?> a = node.find('input')
=> <Capybara::Node::Simple tag="input" path="/html/body/input">

?> a.native
=> #(Element:0x3ff2ad56bf14 {
  name = "input",
  attributes = [
    #(Attr:0x3ff2ad7d94b8 { name = "value", value = "2011-06-18T20:30:00" }),
    #(Attr:0x3ff2ad7d94a4 { name = "type", value = "datetime-local" }),
    #(Attr:0x3ff2ad7d9490 { name = "name", value = "author[forty_two]" }),
    #(Attr:0x3ff2ad7d947c { name = "id", value = "author_forty_two" })]
  })
```

sgruhier/foundation_rails_helper,dsandstrom/foundation_rails_helper