Classify #3464 ChangeLog entry as Bugfix

Signed-off-by: Simon Leet <simon.leet@microsoft.com>
diff --git a/ChangeLog.d/x509write_csr_heap_alloc.txt b/ChangeLog.d/x509write_csr_heap_alloc.txt
index abce20c..6223698 100644
--- a/ChangeLog.d/x509write_csr_heap_alloc.txt
+++ b/ChangeLog.d/x509write_csr_heap_alloc.txt
@@ -1,4 +1,4 @@
-Changes
+Bugfix
    * Reduce the stack consumption of mbedtls_x509write_csr_der() which
      previously could lead to stack overflow on constrained devices.
      Contributed by Doru Gucea and Simon Leet in #3464.