fixed report helper to account for user account timezone

fixed PS-534

Change-Id: I8b5233d80edf179337efdb23e33e959bfda1c72d
Reviewed-on: https://gerrit.instructure.com/24504
Reviewed-by: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brandon Broschinsky <brandonbr@instructure.com>
QA-Review: Brandon Broschinsky <brandonbr@instructure.com>

Author: brandonbr

vendor/plugins/account_reports/lib/canvas/account_reports/report_helper.rb

@@ -43,7 +43,7 @@ def default_timezone_format(datetime, account=root_account)
   # it will then format the datetime using the given format string
   def timezone_strftime(datetime, format)
     if datetime = parse_utc_string(datetime)
-      datetime.strftime(format)
+      (datetime.in_time_zone(account.default_time_zone)).strftime(format)
     end
   end