adding patch
diff --git a/erpnext/patches/v13_0/rename_billable_to_is_billable_in_timesheet.py b/erpnext/patches/v13_0/rename_billable_to_is_billable_in_timesheet.py
new file mode 100644
index 0000000..6860a37
--- /dev/null
+++ b/erpnext/patches/v13_0/rename_billable_to_is_billable_in_timesheet.py
@@ -0,0 +1,7 @@
+from __future__ import unicode_literals
+import frappe
+from frappe.model.utils.rename_field import rename_field
+
+def execute():
+ if "billable" in frappe.db.get_table_columns("Timesheet Detail"):
+ rename_field("Timesheet Detail", "billable", "is_billable")
\ No newline at end of file