Zeitwerk autoload fixes

[mrhardikjoshi]

Fixes #1702

Problem:

1. From Rails application (which uses active_graph but do not explicitly load(require)it ) the neo4j-ruby-driver and other dependacies of active_graph are not loaded. So starting rails environment (by rails s , rails c or any of the rake task) results in uninitialized constant error of that dependancy.

2. generating new rails application using rails new myapp -m activegraph.rb was creating incorrect gemfile.

Solution:

1. Updated railtie.rb to require active_graph gem. The zeitwerk within active_graph will take care of loading all depending files and gems.

2. fixed the template which generated gemfile to use correct operator.

[mrhardikjoshi]

I generated fresh rails application before and after this change to compare exact file difference after this change, here is its diff