remove file must be close it.

in windows if you don't close template file, remove it will raise

WindowsError: [Error 32]

tablib/formats/_dbf.py

@@ -55,6 +55,7 @@ def export_set(dataset):
     else:
         stream = StringIO(dbf_stream.read())
     dbf_stream.close()
+    os.close(temp_file)
     os.remove(temp_uri)
     return stream.getvalue()