rename version to -nullsafety (#33)

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a35d3c1..549b1dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 1.3.0-nnbd
+## 1.3.0-nullsafety
 
 * Migrate to NNBD
 

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 53ba24c..dd4b772 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: typed_data
-version: 1.3.0-nnbd
+version: 1.3.0-nullsafety
 
 description: >-
   Utility functions and classes related to the dart:typed_data library.