chore: add missing changeset

Author: birtles

.changeset/chilly-needles-knock.md

@@ -0,0 +1,16 @@
+---
+'@birchill/bugsnag-zero-lambda-context': minor
+'@birchill/bugsnag-zero': minor
+---
+
+Moved lambda context plugin to a separate package:
+`@birchill/bugsnag-zero-lambda-context`.
+
+If you are using the lambda context plugin, you will need to add the
+`@birchill/bugsnag-zero-lambda-context` package to your dependencies and update
+your import statements.
+
+```diff
+-import { lambdaContext } from '@birchill/bugsnag-zero/lambda-context';
++import { lambdaContext } from '@birchill/bugsnag-zero-lambda-context';
+```