Add ChangeLog entry for _WIN32_WINNT override fix
diff --git a/ChangeLog b/ChangeLog
index 124bd67..9ec996b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,8 @@
 Bugfix
    * Fix redundant declaration of mbedtls_ssl_list_ciphersuites. Raised by
      TrinityTonic. #1359.
+   * Fix for redefinition of _WIN32_WINNT to avoid overriding a definition
+     used by user applications. Found and fixed by Fabio Alessandrelli.
 
 = mbed TLS 2.7.3 branch released 2018-04-30