ChangeLog: Use less confusing version identifier

There can potentially be confusion around what the identifier "2.16.0
xxxx-xx-xx" means. The intent was to communicate that this is a
pre-release version of Mbed TLS 2.16.0 by not specifying the release
date. Instead, use a hopefully more clear identifier,
"2.14.0+01b34fb316a5 xxxx-xx-xx", to show that this is the 2.14.0
release with additional commits from the mbedtls/development branch up
through 01b34fb included.

Author: Patater

ChangeLog

@@ -6,7 +6,7 @@ Changes
    * Add unit tests for AES-GCM when called through mbedtls_cipher_auth_xxx()
      from the cipher abstraction layer. Fixes #2198.
 
-= mbed TLS 2.16.0 branch released xxxx-xx-xx
+= mbed TLS 2.14.0+01b34fb316a5 branch released xxxx-xx-xx
 
 Security
    * Fix timing variations and memory access variations in RSA PKCS#1 v1.5