Sync deployment target with platform min version.

Author: petea

GTMAppAuth.podspec

@@ -37,7 +37,7 @@ requests with AppAuth.
 
   s.osx.source_files = "Source/GTMOAuth2KeychainCompatibility/*.{h,m}",
                        "Source/macOS/**/*.{h,m}"
-  s.osx.deployment_target = '10.9'
+  s.osx.deployment_target = '10.11'
 
   s.tvos.source_files = "Source/iOS/GTMKeychain_iOS.m"
   s.tvos.deployment_target = '9.0'