Fix regression in 1c9b02233631b0ba9b096d79bf5b8d71a370dbb0.

build/write_build_date_header.py

 #!/usr/bin/env 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.
 """Writes a file that contains a define that approximates the build date.
 
 build_type impacts the timestamp generated:
 - default: the build date is set to the most recent first Sunday of a month at
   5:00am. The reason is that it is a time where invalidating the build cache
   shouldn't have major reprecussions (due to lower load).
@@ skipping 76 matching lines @@
   if args.build_date_override:
     # Format is expected to be "Mmm DD YYYY HH:MM:SS".
     build_date = args.build_date_override
   else:
     now = datetime.datetime.utcnow()
     if now.hour < 5:
       # The time is locked at 5:00 am in UTC to cause the build cache
       # invalidation to not happen exactly at midnight. Use the same calculation
       # as the day before.
       # See //base/build_time.cc.
-      now = now - datetime.timedelta(day=1)
+      now = now - datetime.timedelta(days=1)
     now = datetime.datetime(now.year, now.month, now.day, 5, 0, 0)
     build_date = GetBuildDate(args.build_type, now)
 
   output = ('// Generated by //build/write_build_date_header.py\n'
            '#ifndef BUILD_DATE\n'
            '#define BUILD_DATE "{}"\n'
            '#endif // BUILD_DATE\n'.format(build_date))
 
   current_contents = ''
   if os.path.isfile(args.output_file):
     with open(args.output_file, 'r') as current_file:
       current_contents = current_file.read()
 
   if current_contents != output:
     with open(args.output_file, 'w') as output_file:
       output_file.write(output)
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())