Restore missing changelog comment
diff --git a/extensions/ARB/ARB_gl_spirv.txt b/extensions/ARB/ARB_gl_spirv.txt
index a7a4c9a..3931bd5 100644
--- a/extensions/ARB/ARB_gl_spirv.txt
+++ b/extensions/ARB/ARB_gl_spirv.txt
@@ -2122,6 +2122,8 @@
     41    10-Dec-2018    Jon Leech      Use 'workgroup' consistently
                                         throughout (Bug 11723, internal API
                                         issue 87).
+    40    29-May-2018    dgkoch         note post decrement for atomicCounterDecrement
+                                        mapping
     39    25-Apr-2018    JohnK          add mappings of barriers and atomics
     38    10-Apr-2018    dgkoch         OpImageQuerySizeLod and OpImageQuerylevels
                                         only work with Sampled images