[Gemspec] Bump Xcodeproj version

Gemfile.lock

 GIT
   remote: https://github.com/CocoaPods/CLAide.git
-  revision: 44938d0f602fb48e17d5f3b45ecf4764f4fd129d
+  revision: e1edf213a96e72263d18547bfc4f0fa47f81189c
   branch: master
   specs:
     claide (0.5.0)
@@ -18,13 +18,12 @@ GIT
 
 GIT
   remote: https://github.com/CocoaPods/Xcodeproj.git
-  revision: d05d9ee1d43425c177e64a7eb8d2810d491a0c1b
+  revision: e8c929f5e242647590a162477c0f11f65bc8fb2c
   branch: master
   specs:
-    xcodeproj (0.14.1)
+    xcodeproj (0.15.0)
       activesupport (~> 3.0)
       colored (~> 1.2)
-      rake
 
 GIT
   remote: https://github.com/CocoaPods/cocoapods-downloader.git
@@ -79,12 +78,12 @@ PATH
       json_pure (~> 1.8)
       nap (~> 0.5)
       open4 (~> 1.3)
-      xcodeproj (~> 0.14.1)
+      xcodeproj (~> 0.15.0)
 
 GEM
   remote: http://rubygems.org/
   specs:
-    activesupport (3.2.16)
+    activesupport (3.2.17)
       i18n (~> 0.6, >= 0.6.4)
       multi_json (~> 1.0)
     awesome_print (1.2.0)
@@ -118,7 +117,7 @@ GEM
       metaclass (~> 0.0.1)
     mocha-on-bacon (0.2.2)
       mocha (>= 0.13.0)
-    multi_json (1.8.4)
+    multi_json (1.9.2)
     nap (0.6.0)
     netrc (0.7.7)
     notify (0.5.2)
@@ -131,7 +130,7 @@ GEM
     pygments.rb (0.5.4)
       posix-spawn (~> 0.3.6)
       yajl-ruby (~> 1.1.0)
-    rake (10.1.1)
+    rake (10.2.1)
     rb-fsevent (0.9.4)
     rb-inotify (0.9.3)
       ffi (>= 0.5.0)

cocoapods.gemspec

@@ -30,7 +30,7 @@ s.files = Dir["lib/**/*.rb"] + %w{ bin/pod bin/sandbox-pod README.md LICENSE CHA
   s.add_runtime_dependency 'cocoapods-core',            "= #{Pod::VERSION}"
   s.add_runtime_dependency 'claide',                    '~> 0.5.0'
   s.add_runtime_dependency 'cocoapods-downloader',      '~> 0.4.0'
-  s.add_runtime_dependency 'xcodeproj',                 '~> 0.14.1'
+  s.add_runtime_dependency 'xcodeproj',                 '~> 0.15.0'
   s.add_runtime_dependency 'cocoapods-try-release-fix', '~> 0.1.1'
 
   s.add_runtime_dependency 'colored',       '~> 1.2'