Correct documentation of mbedtls_platform_gmtime_r()
Previous documentation stated that gmtime_r() was from the standard library,
but it's POSIX.
diff --git a/include/mbedtls/platform_util.h b/include/mbedtls/platform_util.h
index 38b85b8..164a1a0 100644
--- a/include/mbedtls/platform_util.h
+++ b/include/mbedtls/platform_util.h
@@ -70,7 +70,7 @@
* \brief Platform-specific implementation of gmtime_r()
*
* The function is a thread-safe abstraction that behaves
- * similarly to the gmtime_r() function from the C standard.
+ * similarly to the gmtime_r() function from Unix/POSIX.
*
* Mbed TLS will try to identify the underlying platform and
* make use of an appropriate underlying implementation (e.g.