chore: Update module license header

These modules were imported from the ERPNext codebase into Frappe.
License header was overlooked at that point. These were contributed
initially by Frappe Technologies Pvt Ltd under GPLv3 (ERPNext's license) and now
we, as Frappe Technologies Pvt Ltd converting them to MIT to comply with
Frappe's license.

payments/templates/pages/braintree_checkout.py

@@ -1,5 +1,6 @@
-# Copyright (c) 2018, Frappe Technologies Pvt. Ltd. and Contributors
-# License: GNU General Public License v3. See license.txt
+# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# License: MIT. See LICENSE
+
 import frappe
 from frappe import _
 from frappe.utils import flt

payments/templates/pages/paytm_checkout.py

@@ -1,5 +1,5 @@
-# Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
-# License: GNU General Public License v3. See license.txt
+# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# License: MIT. See LICENSE
 import frappe
 from frappe import _
 import json

payments/templates/pages/razorpay_checkout.py

@@ -1,5 +1,5 @@
-# Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
-# License: GNU General Public License v3. See license.txt
+# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# License: MIT. See LICENSE
 import frappe
 from frappe import _
 from frappe.utils import flt, cint

payments/templates/pages/stripe_checkout.py

@@ -1,5 +1,5 @@
-# Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
-# License: GNU General Public License v3. See license.txt
+# Copyright (c) 2021, Frappe Technologies Pvt. Ltd. and Contributors
+# License: MIT. See LICENSE
 import frappe
 from frappe import _
 from frappe.utils import cint, fmt_money