adding patch

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")