01_bug_report.md: update to match main repo

.github/ISSUE_TEMPLATE/01_bug_report.md

@@ -11,6 +11,7 @@ about: Create a report to help us improve
 - [ ] I made doubly sure this is not a [checksum does not match](https://github.com/Homebrew/homebrew-cask/blob/master/doc/reporting_bugs/a_cask_fails_to_install.md#checksum-does-not-match-error) error.
 - [ ] I ran `brew update-reset && brew update` and retried my command.
 - [ ] I ran `brew doctor`, fixed as many issues as possible and retried my command.
+- [ ] I checked there are no [open issues](https://github.com/Homebrew/homebrew-cask/issues) for the same problem.
 - [ ] I understand that [if I ignore these instructions, my issue may be closed without review](https://github.com/Homebrew/homebrew-cask/blob/master/doc/faq/closing_issues_without_review.md).
 
 #### Description of issue