Fixed stix header test

Author: Bryan Worrell

stix/test/core/stix_header_test.py

@@ -24,7 +24,7 @@ class IdentityTests(EntityTestCase, unittest.TestCase):
     def test_duplicate_package_intent(self):
         # Recreate https://github.com/STIXProject/python-stix/issues/63
         hdr = STIXHeader(package_intents=["Net Defense"])
-        self.assertEqual(1, len(hdr.package_intent))
+        self.assertEqual(1, len(hdr.package_intents))
 
 
 if __name__ == "__main__":