update changelog

Author: dlarocque

firebase-firestore/CHANGELOG.md

@@ -8,7 +8,7 @@
 - [feature] Added support for `rand` and `trunc` Pipeline expressions.
   [#7886](https://github.com/firebase/firebase-android-sdk/pull/7886)
 - [feature] Added support for `isType` Pipeline expression.
-  [#7886](https://github.com/firebase/firebase-android-sdk/pull/7979)
+  [#7985](https://github.com/firebase/firebase-android-sdk/pull/7985)
 
 # 26.1.2