Fix pylint canned check for pylint-2.6.

We were attempting to run pylint-2.6 with python2, when
it needs to be run with python3. I'm not sure how we
haven't noticed this before now.

Bug: 1157676
Change-Id: I60fc22a805c20649d04f7d0f53c828a0db41e8e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3068833Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>

presubmit_canned_checks.py

@@ -932,6 +932,7 @@ def GetPylint(input_api,
   extra_paths_list = extra_paths_list or []
 
   assert version in ('1.5', '2.6'), 'Unsupported pylint version: ' + version
+  python3 = (version == '2.6')
 
   if input_api.is_committing:
     error_type = output_api.PresubmitError
@@ -1018,7 +1019,8 @@ def GetPylint(input_api,
         name='Pylint (%s)' % description,
         cmd=cmd,
         kwargs=kwargs,
-        message=error_type)
+        message=error_type,
+        python3=python3)
 
   # Always run pylint and pass it all the py files at once.
   # Passing py files one at time is slower and can produce