Only run [Transformer.isPrimary] once for each asset/transformer pair.

pkg/barback/CHANGELOG.md

Index: pkg/barback/CHANGELOG.md
diff --git a/pkg/barback/CHANGELOG.md b/pkg/barback/CHANGELOG.md
index 753e5a188c734e80e7a6ec702cc25ba825ad48a8..c62245e920be0dad0681225a1f72486c27f7bc4b 100644
--- a/pkg/barback/CHANGELOG.md
+++ b/pkg/barback/CHANGELOG.md
@@ -1,3 +1,17 @@
+## 0.13.1
+
+* Only run `Transformer.isPrimary` once for each asset.
+
+## 0.13.0
+
+* `Transformer.isPrimary` now takes an `AssetId` rather than an `Asset`.
+
+* `DeclaringTransform` now only exposes the primary input's `AssetId`, rather
+  than the primary `Asset` object.
+
+* `DeclaringTransform` no longer supports `getInput`, `readInput`,
+  `readInputAsString`, or `hasInput`.
+
 ## 0.12.0
 
 * Add a `Transform.logger.fine` function that doesn't print its messages by