ActiveSupport::TimeZone gives incorrect offset during Daylight Savings Time

Here is one example:
```
> pdt = ActiveSupport::TimeZone.new("Pacific Time (US & Canada)")
=> (GMT-08:00) Pacific Time (US & Canada)
> pdt.formatted_offset
=> "-08:00"
> pdt.now.formatted_offset
=> "-07:00"
```
date was being incorrectly converted in such cases.