Fix link in DTLSSocket.md

Fix broken link.

Author: Amanda Butler

docs/api/networksocket/DTLSSocket.md

@@ -16,7 +16,7 @@ To use secure DTLS connections, application use the `DTLSSocketWrapper` through
 
 Please see the TLSSocket example:
 
-[![View code](https://www.mbed.com/embed/?url=https://github.com/ARMmbed/mbed-os-example-tls-socket/blob/master/)](https://github.com/ARMmbed/mbed-os-example-tls-socket/blob/mbed-os-5.12/main.cpp)
+[![View code](https://www.mbed.com/embed/?url=https://github.com/ARMmbed/mbed-os-example-tls-socket/blob/master/)](https://github.com/ARMmbed/mbed-os-example-tls-socket/blob/mbed-os-5.14/main.cpp)
 
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