Fix Python2.6 coverage.

tests/trailing_whitespace_fixer_test.py

diff --git a/tests/trailing_whitespace_fixer_test.py b/tests/trailing_whitespace_fixer_test.py
index 9a6cd03..f698633 100644
--- a/tests/trailing_whitespace_fixer_test.py
+++ b/tests/trailing_whitespace_fixer_test.py
@@ -9,8 +9,7 @@
             ('foo.py', 'foo \nbar \n'),
             ('bar.py', 'bar\t\nbaz\t\n'),
         ):
-            with open(filename, 'w') as file_obj:
-                file_obj.write(contents)
+            open(filename, 'w').write(contents)
 
         ret = fix_trailing_whitespace(['foo.py', 'bar.py'])
         assert ret == 1