added a placeholder to select in category widget on reports page
fixed the indentation in includes/admin/reports/class-wc-report-sales-by-category.php
fixed some coding standards in includes/admin/reports/class-wc-report-sales-by-category.php
Merge pull request #4555 from claudiosmweb/added_placeholder_for_category_reports

Fixed untranslatable string in reports by category