Update Gemfile mingw > windows

[ns-rse]

On building locally I see the following warning...

❱ bundle exec jekyll serve
Could not find gem 'github-pages' in locally installed gems.
Run `bundle install` to install missing gems.
❱ bundle install
[DEPRECATED] Platform :mingw, :mswin, :x64_mingw will be removed in the future. Please use platform :windows instead.

The Gemfile contains

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

Because of the pending deprication this should probably be converted to...

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:windows, :jruby]