rake about database adapter inconsistent with database.yml

In `database.yml` (rails-generated default file): ``` default: &default adapter: sqlite3 pool: 5 timeout: 5000 development: <<: *default database: db/development.sqlite3 test: <<: *default database: db/test.sqlite3 production: <<: *default database: db/production.sqlite3 ``` When running `rake about`, I have this error: ``` Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord). ``` If I add the `pg` gem, then `rake about` gives this output: ``` About your application's environment Ruby version 2.1.0-p0 (x86_64-darwin13.0) RubyGems version 2.2.2 Rack version 1.5 Rails version 4.1.0 JavaScript Runtime Node.js (V8) Active Record version 4.1.0 Action Pack version 4.1.0 Action View version 4.1.0 Action Mailer version 4.1.0 Active Support version 4.1.0 Middleware Rack::Sendfile, ActionDispatch::Static, Rack::Lock, # <ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x007f8043154a30>, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ParamsParser, Rack::Head, Rack::ConditionalGet, Rack::ETag Environment development Database adapter postgresql Database schema version 0 ``` Any idea why this is happening? I want to use the sqlite3 adapter.