[docs] fix info about default Thread version supported by OpenThread (o…

…penthread#6689)

After changed the default Thread version, the description about it has
not been updated. This commit fixes it.

examples/README.md

@@ -60,7 +60,7 @@ This page lists the available common switches with description. Unless stated ot
 | SPINEL_ENCRYPTER_LIBS | not implemented | Specifies library files (absolute paths) for implementing the NCP Spinel Encrypter. |
 | SRP_CLIENT | OT_SRP_CLIENT | Enable support for SRP client. |
 | SRP_SERVER | OT_SRP_SERVER | Enable support for SRP server. |
-| THREAD_VERSION | OT_THREAD_VERSION | Enables the chosen Thread version (1.1 (default) / 1.2). For example, set to `1.2` for Thread 1.2. |
+| THREAD_VERSION | OT_THREAD_VERSION | Enables the chosen Thread version (1.1 / 1.2 (default)). For example, set to `1.1` for Thread 1.1. |
 | TIME_SYNC | OT_TIME_SYNC | Enables the time synchronization service feature. **Note: Enabling this feature breaks conformance to the Thread Specification.** |  |
 | TREL | OT_TREL | Enables TREL radio link for Thread over Infrastructure feature. |
 | UDP_FORWARD | OT_UDP_FORWARD | Enables support for UDP forward. | Enable this switch on the Border Router device (running on the NCP design) with External Commissioning support to service Thread Commissioner packets on the NCP side. |