foundation_rails_helper.gemspec: updated tzinfo version for Rails 4.1.rc1 compatibility.

without this i get the following error when trying to install current master in my Gemfile in a Rails 4.1.rc1 project:

Gemfile:
`gem 'foundation_rails_helper', github: 'sgruhier/foundation_rails_helper'`

`bundle update foundation_rails_helper` returns:

```
Bundler could not find compatible versions for gem "tzinfo":
In Gemfile:
foundation_rails_helper (>= 0) ruby depends on
tzinfo (~> 0.3.37) ruby

rails (~> 4.1.0.rc1) ruby depends on
  tzinfo (1.1.0)
```