update CHANGELOG.md for v8.1.3 [skip ci]

Signed-off-by: Christopher Hiller <[email protected]>

Author: boneskull

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 8.1.3 / 2020-08-28
+
+## :bug: Fixes
+
+- #4425: Restore `Mocha.utils.lookupFiles()` and Webpack compatibility (both broken since v8.1.0); `Mocha.utils.lookupFiles()` is now **deprecated** and will be removed in the next major revision of Mocha; use `require('mocha/lib/cli').lookupFiles` instead (@boneskull)
+
 # 8.1.2 / 2020-08-25
 
 ## :bug: Fixes