Include common commands in rails help output

With their descriptions commented out these commands were not included
in the rails help command's output, which is a shame as they are useful,
particularly during the development of more complex migrations.

activerecord/lib/active_record/railties/databases.rake

@@ -112,7 +112,7 @@ db_namespace = namespace :db do
       end
     end
 
-    # desc  'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
+    desc "Rolls back the database one migration and re-migrates up (options: STEP=x, VERSION=x)."
     task redo: :load_config do
       raise "Empty VERSION provided" if ENV["VERSION"] && ENV["VERSION"].empty?
 
@@ -128,7 +128,7 @@ db_namespace = namespace :db do
     # desc 'Resets your database using your migrations for the current environment'
     task reset: ["db:drop", "db:create", "db:migrate"]
 
-    # desc 'Runs the "up" for a given migration VERSION.'
+    desc 'Runs the "up" for a given migration VERSION.'
     task up: :load_config do
       ActiveRecord::Tasks::DatabaseTasks.raise_for_multi_db(command: "db:migrate:up")
 
@@ -162,7 +162,7 @@ db_namespace = namespace :db do
       end
     end
 
-    # desc 'Runs the "down" for a given migration VERSION.'
+    desc 'Runs the "down" for a given migration VERSION.'
     task down: :load_config do
       ActiveRecord::Tasks::DatabaseTasks.raise_for_multi_db(command: "db:migrate:down")
 
@@ -230,7 +230,7 @@ db_namespace = namespace :db do
     db_namespace["_dump"].invoke
   end
 
-  # desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
+  desc "Drops and recreates the database from db/schema.rb for the current environment and loads the seeds."
   task reset: [ "db:drop", "db:setup" ]
 
   # desc "Retrieves the charset for the current environment's database"