Merge null-safety plugins (#3324)

packages/plugin_platform_interface/CHANGELOG.md

diff --git a/packages/plugin_platform_interface/CHANGELOG.md b/packages/plugin_platform_interface/CHANGELOG.md
index 01b5ff7..7df1834 100644
--- a/packages/plugin_platform_interface/CHANGELOG.md
+++ b/packages/plugin_platform_interface/CHANGELOG.md
@@ -1,3 +1,11 @@
+## 1.1.0-nullsafety.1
+
+* Bump Dart SDK to support null safety.
+
+## 1.1.0-nullsafety
+
+* Migrate to null safety.
+
 ## 1.0.3
 
 * Fix homepage in `pubspec.yaml`.