Gemfile in dm-do-adapter-1.2.0.rc1 vs Gemfile in dm-do-adapter-1.2.0.rc2

@@ -1,19 +1,22 @@
 require 'pathname'
 
 source 'http://rubygems.org'
 
-SOURCE       = ENV.fetch('SOURCE', :git).to_sym
-REPO_POSTFIX = SOURCE == :path ? ''                                : '.git'
-DATAMAPPER   = SOURCE == :path ? Pathname(__FILE__).dirname.parent : 'http://github.com/datamapper'
-DM_VERSION   = '~> 1.2.0.rc1'
-DO_VERSION   = '~> 0.10.6'
+SOURCE         = ENV.fetch('SOURCE', :git).to_sym
+REPO_POSTFIX   = SOURCE == :path ? ''                                : '.git'
+DATAMAPPER     = SOURCE == :path ? Pathname(__FILE__).dirname.parent : 'http://github.com/datamapper'
+DM_VERSION     = '~> 1.2.0.rc2'
+DO_VERSION     = '~> 0.10.6'
+CURRENT_BRANCH = ENV.fetch('GIT_BRANCH', 'master')
 
 do_options = {}
 do_options[:git] = "#{DATAMAPPER}/do#{REPO_POSTFIX}" if ENV['DO_GIT'] == 'true'
 
 gem 'data_objects', DO_VERSION, do_options.dup
-gem 'dm-core',      DM_VERSION, SOURCE => "#{DATAMAPPER}/dm-core#{REPO_POSTFIX}"
+gem 'dm-core', DM_VERSION,
+  SOURCE  => "#{DATAMAPPER}/dm-core#{REPO_POSTFIX}",
+  :branch => CURRENT_BRANCH
 
 group :development do
 
   gem 'jeweler', '~> 1.6.4'
   gem 'rake',    '~> 0.9.2'