Merge pull request #392 from mariocesar/use_django_namedtemporaryfile

Uses the NamedTemporaryFile class provided by Django

sorl/thumbnail/engines/convert_engine.py

@@ -2,9 +2,9 @@
 import re
 import os
 import subprocess
-from tempfile import NamedTemporaryFile
 
 from django.utils.encoding import smart_str
+from django.core.files.temp import NamedTemporaryFile
 
 from sorl.thumbnail.base import EXTENSIONS
 from sorl.thumbnail.compat import b