[gemspec] Bump Xcodeproj dep to 0.2.3

cocoapods.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'json',          '~> 1.7.3'
   s.add_runtime_dependency 'open4',         '~> 1.3.0'
   s.add_runtime_dependency 'rake',          '~> 0.9.0'
-  s.add_runtime_dependency 'xcodeproj',     '~> 0.2.2'
+  s.add_runtime_dependency 'xcodeproj',     '~> 0.2.3'
   s.add_runtime_dependency 'activesupport', '~> 3.2.6'
 
   s.add_development_dependency 'bacon', '~> 1.1'