[1.6.x] Fix an encoding preamble so the tests pass on 2.7.9.

It seems there was a change in the parsing of encoding preambles in Python
2.7.9, compared to previous 2.7.x Pythons. This is a backport of the only piece
of e520a73eee that's needed to prevent an import
failure under 2.7.9.

tests/utils_tests/test_jslex.py

@@ -1,5 +1,5 @@
-"""Tests for jslex."""
 # encoding: utf-8
+"""Tests for jslex."""
 # originally from https://bitbucket.org/ned/jslex
 
 from django.test import TestCase