rev to a dev version

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cc86fd..44d987f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+## 0.2.1-dev
+
 ## 0.2.0
 
 * Migrate to null safety.

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 18862fd..74b41e2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: http_retry
-version: 0.2.0
+version: 0.2.1-dev
 description: >-
   A wrapper for package:http clients that automatically retries requests
 repository: https://github.com/dart-lang/http_retry