[docs] update Thread version (#8053)

NOTICE

@@ -1,16 +1,16 @@
-OpenThread is an open source implementation of the Thread 1.2.0 Final Specification.
-The Thread 1.2.0 Final Specification is promulgated by the Thread Group. The Thread
+OpenThread is an open source implementation of the Thread 1.3.0 Final Specification.
+The Thread 1.3.0 Final Specification is promulgated by the Thread Group. The Thread
 Group is a non-profit organization formed for the purposes of defining one or
 more specifications, best practices, reference architectures, implementation
 guidelines and certification programs to promote the availability of compliant
 implementations of the Thread protocol. Information on becoming a Member, including
 information about the benefits thereof, can be found at http://threadgroup.org.
 
 OpenThread is not affiliated with or endorsed by the Thread Group. Implementation
-of this OpenThread code does not assure compliance with the Thread 1.2.0 Final
+of this OpenThread code does not assure compliance with the Thread 1.3.0 Final
 Specification and does not convey the right to identify any final product as Thread
 certified. Members of the Thread Group may hold patents and other intellectual
-property rights relating to the Thread 1.2.0 Final Specification, ownership and
+property rights relating to the Thread 1.3.0 Final Specification, ownership and
 licenses of which are subject to the Thread Group’s IP Policies, and not this license.
 
 The included copyright to the OpenThread code is subject to the license in the

README.md

@@ -10,7 +10,7 @@ OpenThread released by Google is... <a href="https://www.threadgroup.org/What-is
 
 **...OS and platform agnostic**, with a narrow platform abstraction layer and a small memory footprint, making it highly portable. It supports both system-on-chip (SoC) and network co-processor (NCP) designs.
 
-**...a Thread Certified Component**, implementing all features defined in the [Thread 1.2 specification](https://www.threadgroup.org/support#specifications), including all Thread networking layers (IPv6, 6LoWPAN, IEEE 802.15.4 with MAC security, Mesh Link Establishment, Mesh Routing) and device roles, as well as [Border Router](https://github.com/openthread/ot-br-posix) support.
+**...a Thread Certified Component**, implementing all features defined in the [Thread 1.3.0 specification](https://www.threadgroup.org/support#specifications), including all Thread networking layers (IPv6, 6LoWPAN, IEEE 802.15.4 with MAC security, Mesh Link Establishment, Mesh Routing) and device roles, as well as [Border Router](https://github.com/openthread/ot-br-posix) support.
 
 More information about Thread can be found at [threadgroup.org](http://threadgroup.org/). Thread is a registered trademark of the Thread Group, Inc.