Add option to restrict overriding authorize_options by user request

[tnantoka]

Thank you for the great gem!

By the following implementation, all authorize_options can be overridden with request parameters.

omniauth-google-oauth2/lib/omniauth/strategies/google_oauth2.rb

Lines 34 to 36 in 8bebf08

	options[:authorize_options].each do |k|
	params[k] = request.params[k.to_s] unless [nil, ''].include?(request.params[k.to_s])
	end

For example, even if we restrict it with hd: 'exanple.com', end-users can use any hd with /oauth/google_oauth2?hd=example.net.
It's flexible and convenient, but it may be unexpected behavior in some apps.

I have added an option to control this behavior with this pull request.
If you don't need this change, feel free to close it.

Thanks,

[zquestz]

Thanks, decided this should go in. Appreciate the work. =)