security: Change default osx keychain from NDN to login

Change-Id: Ia3391ec2d83ec69f2d4594838385ce0ff2ecdf81
diff --git a/src/security/identity/osx-private-key-storage.cpp b/src/security/identity/osx-private-key-storage.cpp
index adf3542..3f11c04 100644
--- a/src/security/identity/osx-private-key-storage.cpp
+++ b/src/security/identity/osx-private-key-storage.cpp
@@ -30,7 +30,7 @@
   class OSXPrivateKeyStorage::Impl {
   public:
     Impl(const std::string &keychainName)
-      : keyChainName_ ("" == keychainName ?  "NDN.keychain" : keychainName)
+      : keyChainName_ ("" == keychainName ?  "login.keychain" : keychainName)
     {
     }