Update comments for net/data/verify_certificate_chain_unittest/

net/data/verify_certificate_chain_unittest/expired-root/generate-chains.py

 #!/usr/bin/python
 # Copyright (c) 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-"""Certificate chain with a root, intermediate and target. The root has a
-smaller validity range than the other certificates, making it easy to violate
-just its validity.
+"""Certificate chain where the root has a smaller validity range than the other
+certificates, making it easy to violate just its validity.
 
   Root:          2015/03/01 -> 2015/09/01
   Intermediate:  2015/01/01 -> 2016/01/01
   Target:        2015/01/01 -> 2016/01/01
 """
 
 
 import sys
 sys.path += ['..']
 
 import common
 
 # Self-signed root certificate.
 root = common.create_self_signed_root_certificate('Root')
 root.set_validity_range(common.MARCH_1_2015_UTC, common.SEPTEMBER_1_2015_UTC)
 
 # Intermediate certificate.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 intermediate.set_validity_range(common.JANUARY_1_2015_UTC,
                                 common.JANUARY_1_2016_UTC)
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 target.set_validity_range(common.JANUARY_1_2015_UTC, common.JANUARY_1_2016_UTC)
 
 chain = [target, intermediate, root]
 common.write_chain(__doc__, chain, 'chain.pem')