Exception loading pg adapter in lotus example

gistfile1.txt

Boot Error

Something went wrong while loading /home/darwinrc/dev/kommit/lotustest/config.ru
RuntimeError: Cannot instantiate adapter of Lotus::Model::Adapters::SqlAdapter (LoadError: cannot load such file -- pg)

/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model/config/adapter.rb:101:in `rescue in instantiate_adapter'
/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model/config/adapter.rb:95:in `instantiate_adapter'
/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model/config/adapter.rb:81:in `build'
/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model/configuration.rb:168:in `_build_adapter'
/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model/configuration.rb:59:in `load!'
/var/lib/gems/2.1.0/gems/lotus-model-0.2.3/lib/lotus/model.rb:76:in `load!'
/home/darwinrc/dev/kommit/lotustest/lib/lotustest.rb:39:in `<top (required)>'
/home/darwinrc/dev/kommit/lotustest/config/environment.rb:4:in `require_relative'
/home/darwinrc/dev/kommit/lotustest/config/environment.rb:4:in `<top (required)>'
/home/darwinrc/dev/kommit/lotustest/config.ru:1:in `require'
/home/darwinrc/dev/kommit/lotustest/config.ru:1:in `block in inner_app'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `instance_eval'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `initialize'
/home/darwinrc/dev/kommit/lotustest/config.ru:1:in `new'
/home/darwinrc/dev/kommit/lotustest/config.ru:1:in `inner_app'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:112:in `eval'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:112:in `inner_app'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:102:in `assemble_app'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:86:in `proceed_as_child'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:31:in `call!'
/var/lib/gems/2.1.0/gems/shotgun-0.9/lib/shotgun/loader.rb:18:in `call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/lint.rb:49:in `_call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/lint.rb:37:in `call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/showexceptions.rb:24:in `call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/commonlogger.rb:33:in `call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/content_length.rb:15:in `call'
/var/lib/gems/2.1.0/gems/rack-1.6.0/lib/rack/handler/webrick.rb:89:in `service'
/usr/lib/ruby/2.1.0/webrick/httpserver.rb:138:in `service'
/usr/lib/ruby/2.1.0/webrick/httpserver.rb:94:in `run'
/usr/lib/ruby/2.1.0/webrick/server.rb:295:in `block in start_thread'