Widen deps range on built_value to allow null safety. (#306)

* Widen deps range on built_value to allow null safety.

* pubspec and changelog

Co-authored-by: Nate Bosch <nbosch@google.com>

Author: davidmorgan

CHANGELOG.md

@@ -1,4 +1,7 @@
-* Added support for `extension` methods.
+## 3.6.0
+
+* Add support for creating `extension` methods.
+* Expand constraint on `built_value` to allow null safe migrated version.
 
 ## 3.5.0
 

pubspec.yaml

@@ -1,5 +1,5 @@
 name: code_builder
-version: 3.5.0
+version: 3.6.0
 
 description: >-
   A fluent, builder-based library for generating valid Dart code
@@ -9,8 +9,8 @@ environment:
   sdk: '>=2.7.0 <3.0.0'
 
 dependencies:
-  built_collection: '>=3.0.0 <5.0.0'
-  built_value: ^7.0.0
+  built_collection: '>=3.0.0 <6.0.0'
+  built_value: '>=7.0.0 <9.0.0'
   collection: ^1.14.0
   matcher: ^0.12.0
   meta: ^1.0.5