[Gemspec] Bump Xcodeproj

CHANGELOG.md

+## 0.17.0.rc3
+[CocoaPods](https://github.com/CocoaPods/CocoaPods/compare/0.17.0.rc1...0.17.0.rc2
+• [Xcodeproj](https://github.com/CocoaPods/Xcodeproj/compare/0.5.0...0.5.1))
+
+###### Bug fixes
+
+- Fixed and issue which prevent the inclusion of OTHER_CFLAGS and
+  OTHER_CPLUSPLUSFLAGS  in the release builds of the Pods project.
+
 ## 0.17.0.rc2
 [CocoaPods](https://github.com/CocoaPods/CocoaPods/compare/0.17.0.rc1...0.17.0.rc2)
 • [cocoapods-core](https://github.com/CocoaPods/Core/compare/0.17.0.rc1...0.17.0.rc2)

cocoapods.gemspec

@@ -30,7 +30,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'cocoapods-core',       "= #{Pod::VERSION}"
   s.add_runtime_dependency 'claide',               '~> 0.2.0'
   s.add_runtime_dependency 'cocoapods-downloader', '~> 0.1.0'
-  s.add_runtime_dependency 'xcodeproj',            '~> 0.5.0'
+  s.add_runtime_dependency 'xcodeproj',            '~> 0.5.1'
 
   s.add_runtime_dependency 'faraday',       '~> 0.8.1'
   s.add_runtime_dependency 'octokit',       '~> 1.7'