rename version to -nullsafety (#146)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a47241..935c5ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 1.15.0-nnbd
+## 1.15.0-nullsafety
 
 Pre-release for the null safety migration of this package.
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 638740b..42cf9b5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: collection
-version: 1.15.0-nnbd
+version: 1.15.0-nullsafety
 
 description: Collections and utilities functions and classes related to collections.
 homepage: https://www.github.com/dart-lang/collection