Add change log entry for mbedtls_ssl_config_free() fix
mbed TLS ChangeLog (Sorted per branch, date)
+= mbed TLS 2.x.x branch released xxxx-xx-xx
+
+Changes
+ * Fix possible memory leak in mbedtls_ssl_config_free().
+ by junyeonLEE <dlwnsdus2@naver.com>
+
= mbed TLS 2.7.x branch released 2018-xx-xx
Default behavior changes
