Getting error while migrating db in ruby on rails project on windows 7, with ruby 2.3.3 and rails 4.2.5.2

I am getting below errors on prelauch project on github. I have install postgres db but i am not getting which gem is having PGconn , PGresult and PGerror.

The PGconn, PGresult, and PGError constants are deprecated, and will be removed as of version 1.0.   You should use PG::Connection, PG::Result, and PG::Errenter code hereor instead, respectively.enter code here

Called from C:/Ruby23/lib/ruby/gems/2.3.0/gems/activesupport-4.2.5.2/lib/active_support/dependencies.rb:240:in `load_dependency
'
== 20130127063936 DeviseCreateAdminUsers: migrating ===========================
-- create_table(:admin_users)
   -> 0.2293s
-- add_index(:admin_users, :email, {:unique=>true})
   -> 0.0638s
-- add_index(:admin_users, :reset_password_token, {:unique=>true})
   -> 0.0658s

== 20130127063936 DeviseCreateAdminUsers: migrated (0.3603s) ==================
 
rake aborted!
LoadError: cannot load such file -- bcrypt_ext
D:/Projects/prelaunchr/db/migrate/20130127063936_devise_create_admin_users.rb:5:in `migrate'
C:in `migrate'
LoadError: cannot load such file -- 2.3/bcrypt_ext

D:/Projects/prelaunchr/db/migrate/20130127063936_devise_create_admin_users.rb:5:in migrate' C:in migrate' Tasks: TOP => db:migrate (See full trace by running task with --trace)

Ruby version: 2.3.3
Rails version : 4.2.5.2