allow the null safe built_* package versions (#2967)

Does not regenerate code - the old code is compatible with the new libs but the reverse is not true.

Author: jakemac53

build_daemon/CHANGELOG.md

@@ -1,3 +1,9 @@
+# 2.1.5-dev
+
+- Allow the null safe built_collection, and built_value, but keep the old
+  built_value_generator and generated code which is compatible across both
+  versions of the core libs.
+
 # 2.1.4
 
 - Remove dependency on `package:package_resolver`.

build_daemon/pubspec.yaml

@@ -1,14 +1,14 @@
 name: build_daemon
-version: 2.1.4
+version: 2.1.5-dev
 description: A daemon for running Dart builds.
 homepage: https://github.com/dart-lang/build/tree/master/build_daemon
 
 environment:
   sdk: ">=2.9.0 <3.0.0"
 
 dependencies:
-  built_collection: ^4.1.0
-  built_value: ^7.0.0
+  built_collection: '>=4.1.0 <6.0.0'
+  built_value: '>=7.0.0 <9.0.0'
   http_multi_server: ^2.0.0
   logging: ^0.11.0
   pedantic: ^1.0.0