Remove dict comprehension to support python 2.6 in tests

Author: Peter Grant

tests/test_jwt.py

@@ -44,8 +44,8 @@ def test_non_default_headers(self, claims, key, headers):
         decoded = jwt.decode(encoded, key)
         assert claims == decoded
         all_headers = jwt.get_unverified_headers(encoded)
-        custom_headers = {k: all_headers[k] for k in headers.keys()}
-        assert custom_headers == headers
+        for k, v in headers.items():
+            assert all_headers[k] == v
 
     def test_encode(self, claims, key):