fix warning

Author: dstansby

docs/release-notes.rst

@@ -8,7 +8,7 @@ Release notes
 
 .. warning::
 
-    In versions 3.0.0 to 3.0.7 opening arrays with ``mode='a'`` (the default for many builtin functions)
+    In versions 3.0.0 to 3.0.7 opening arrays or groups with ``mode='a'`` (the default for many builtin functions)
     would cause any existing paths in the store to be deleted. This is fixed in 3.0.8, and
     we recommend all users upgrade to avoid this bug that could cause unintentional data loss.