Python 3.9a5 removed xml.etree.cElementTree

It was deprecated since Python 3.3.

Fixes #112.

check_manifest.py

@@ -33,7 +33,12 @@
 from distutils.filelist import glob_to_re
 from contextlib import contextmanager, closing
 from distutils.text_file import TextFile
-from xml.etree import cElementTree as ET
+
+try:
+    from xml.etree import cElementTree as ET
+except ImportError:
+    # Python 3.9+
+    from xml.etree import ElementTree as ET
 
 try:
     import ConfigParser

tests.py

@@ -14,7 +14,7 @@
 import zipfile
 from contextlib import closing
 from io import BytesIO
-from xml.etree import cElementTree as ET
+from xml.etree import ElementTree as ET
 
 try:
     from cStringIO import StringIO  # Python 2.x