Use bin/rails in generator Base banner

The banner for `bin/rails generate` and some related documentation were
updated [recently][1], however `bin/rails generate controller` did not
actually include `bin/rails` in its usage.

[1]: f7204d8

Author: skipkayhil

railties/lib/rails/generators/base.rb

@@ -327,7 +327,7 @@ def namespaced_path # :doc:
 
         # Use Rails default banner.
         def self.banner # :doc:
-          "rails generate #{namespace.delete_prefix("rails:")} #{arguments.map(&:usage).join(' ')} [options]".gsub(/\s+/, " ")
+          "bin/rails generate #{namespace.delete_prefix("rails:")} #{arguments.map(&:usage).join(' ')} [options]".gsub(/\s+/, " ")
         end
 
         # Sets the base_name taking into account the current class namespace.

railties/test/generators_test.rb

@@ -152,12 +152,12 @@ def test_rails_generators_does_not_show_active_record_hooks
 
   def test_default_banner_should_show_generator_namespace
     klass = Rails::Generators.find_by_namespace(:foobar)
-    assert_match(/^rails generate foobar:foobar/, klass.banner)
+    assert_match(/^bin\/rails generate foobar:foobar/, klass.banner)
   end
 
   def test_default_banner_should_not_show_rails_generator_namespace
     klass = Rails::Generators.find_by_namespace(:model)
-    assert_match(/^rails generate model/, klass.banner)
+    assert_match(/^bin\/rails generate model/, klass.banner)
   end
 
   def test_no_color_sets_proper_shell