tools: define xrange() in Python 3

__xrange()__ was removed in Python 3 in favor of __range()__.
This PR ensures similar functionality on both Python 2 and Python 3.

Discovered via https://travis-ci.com/nodejs/node/builds/79706150
(https://github.com/nodejs/node/pull/21942).

PR-URL: https://github.com/nodejs/node/pull/21945
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/cpplint.py

@@ -53,6 +53,11 @@ import string
 import sys
 import unicodedata
 
+try:
+  xrange
+except NameError:
+  xrange = range
+
 
 logger = logging.getLogger('testrunner')