[gemspec] Bump Xcodeproj to `~> 0.21.0`

Gemfile.lock

@@ -24,10 +24,10 @@ GIT
 
 GIT
   remote: https://github.com/CocoaPods/Xcodeproj.git
-  revision: 8bf91f215cb996f36c4028c78b033d1ea6b6f1fc
+  revision: 2ef226943bf432aef0b610fcbe8b99e9ae9ef1f8
   branch: master
   specs:
-    xcodeproj (0.20.2)
+    xcodeproj (0.21.0)
       activesupport (>= 3)
       colored (~> 1.2)
 
@@ -78,16 +78,16 @@ PATH
       molinillo (~> 0.1.2)
       nap (~> 0.8)
       open4 (~> 1.3)
-      xcodeproj (~> 0.20.2)
+      xcodeproj (~> 0.21.0)
 
 GEM
   remote: http://rubygems.org/
   specs:
-    activesupport (4.1.8)
-      i18n (~> 0.6, >= 0.6.9)
+    activesupport (4.2.0)
+      i18n (~> 0.7)
       json (~> 1.7, >= 1.7.7)
       minitest (~> 5.1)
-      thread_safe (~> 0.1)
+      thread_safe (~> 0.3, >= 0.3.4)
       tzinfo (~> 1.1)
     addressable (2.3.6)
     ast (2.0.0)
@@ -107,7 +107,7 @@ GEM
     escape (0.0.4)
     ffi (1.9.6)
     fuzzy_match (2.0.4)
-    i18n (0.6.11)
+    i18n (0.7.0)
     json (1.7.7)
     kicker (3.0.0)
       listen (~> 1.3.0)
@@ -118,7 +118,7 @@ GEM
       rb-kqueue (>= 0.2)
     metaclass (0.0.4)
     method_source (0.8.2)
-    minitest (5.4.3)
+    minitest (5.5.0)
     mocha (1.1.0)
       metaclass (~> 0.0.1)
     mocha-on-bacon (0.2.2)

cocoapods.gemspec

@@ -29,7 +29,7 @@ Gem::Specification.new do |s|
   # Link with the version of CocoaPods-Core
   s.add_runtime_dependency 'cocoapods-core',       "= #{Pod::VERSION}"
   s.add_runtime_dependency 'claide',               '~> 0.7.0'
-  s.add_runtime_dependency 'xcodeproj',            '~> 0.20.2'
+  s.add_runtime_dependency 'xcodeproj',            '~> 0.21.0'
   s.add_runtime_dependency 'cocoapods-downloader', '~> 0.8.0'
   s.add_runtime_dependency 'cocoapods-plugins',    '~> 0.3.1'
   s.add_runtime_dependency 'cocoapods-try',        '~> 0.4.2'