bin/generator: Write slug of last run generator to a file.
bin/generator: Write slug of last run generator to a file.

The name of the generator will be written to the `.last_generator_run`
file.

This is useful for scripting and recovering from generator failures.

NeimadTL/ruby,Insti/exercism-ruby,Insti/exercism-ruby,Insti/xruby,Insti/xruby,NeimadTL/ruby,exercism/xruby,Insti/exercism-ruby,exercism/xruby,NeimadTL/ruby