The banner for this class.
You can customize it if you are invoking the thor class by another ways
which is not the Bundler::Thor::Runner. It receives the
command that is going to be invoked and a boolean which indicates if the
namespace should be displayed as arguments.
# File lib/bundler/vendor/thor/lib/thor.rb, line 395
def banner(command, namespace = nil, subcommand = false)
"#{basename} #{command.formatted_usage(self, $thor_runner, subcommand)}"
end