Fixes #150

rest_framework does not have serializers object so needs an explicit
import. Added the import into the >=3.0 code only so does not affect
older DRF versions if this is something new.

Author: mikebiglan

rest_framework_jwt/compat.py

@@ -9,6 +9,7 @@
     class PasswordField(CharField):
         widget = widgets.PasswordInput
 else:
+    import rest_framework.serializers
     class Serializer(rest_framework.serializers.Serializer):
         @property
         def object(self):