prepare for the 2.9 stable sdk release of package:collection (#148)

Updates the sdk constraint to <=2.9.10
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ae30a1..93b4bf9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,6 @@
-## 1.15.0-nullsafety.1-dev
+## 1.15.0-nullsafety.1
+
+* Allow the <=2.9.10 stable sdks.
 
 ## 1.15.0-nullsafety
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 261c629..9569802 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,11 +1,11 @@
 name: collection
-version: 1.15.0-nullsafety.1-dev
+version: 1.15.0-nullsafety.1
 
 description: Collections and utilities functions and classes related to collections.
 homepage: https://www.github.com/dart-lang/collection
 
 environment:
-  sdk: '>=2.9.0-20.0 <2.9.0'
+  sdk: '>=2.9.0-20.0 <=2.9.10'
 
 dev_dependencies:
   pedantic: ^1.0.0
@@ -13,82 +13,51 @@
 
 dependency_overrides:
   async:
-    git:
-      url: git://github.com/dart-lang/async.git
-      ref: null_safety
+    git: git://github.com/dart-lang/async.git
   boolean_selector:
-    git:
-      url: git://github.com/dart-lang/boolean_selector.git
-      ref: null_safety
+    git: git://github.com/dart-lang/boolean_selector.git
   charcode:
-    git:
-      url: git://github.com/dart-lang/charcode.git
-      ref: null_safety
+    git: git://github.com/dart-lang/charcode.git
   js:
     git:
       url: git://github.com/dart-lang/sdk.git
       path: pkg/js
   matcher:
-    git:
-      url: git://github.com/dart-lang/matcher.git
-      ref: null_safety
+    git: git://github.com/dart-lang/matcher.git
   meta:
     git:
       url: git://github.com/dart-lang/sdk.git
-      ref: null_safety-pkgs
       path: pkg/meta
   path:
-    git:
-      url: git://github.com/dart-lang/path.git
-      ref: null_safety
+    git: git://github.com/dart-lang/path.git
   pedantic:
-    git:
-      url: git://github.com/dart-lang/pedantic.git
-      ref: null_safety
+    git: git://github.com/dart-lang/pedantic.git
   pool:
-    git:
-      url: git://github.com/dart-lang/pool.git
-      ref: null_safety
+    git: git://github.com/dart-lang/pool.git
   source_maps:
-    git:
-      url: git://github.com/dart-lang/source_maps.git
-      ref: null_safety
+    git: git://github.com/dart-lang/source_maps.git
   source_map_stack_trace:
-    git:
-      url: git://github.com/dart-lang/source_map_stack_trace.git
-      ref: null_safety
+    git: git://github.com/dart-lang/source_map_stack_trace.git
   source_span:
-    git:
-      url: git://github.com/dart-lang/source_span.git
-      ref: null_safety
+    git: git://github.com/dart-lang/source_span.git
   stack_trace:
-    git:
-      url: git://github.com/dart-lang/stack_trace.git
-      ref: null_safety
+    git: git://github.com/dart-lang/stack_trace.git
   stream_channel:
-    git:
-      url: git://github.com/dart-lang/stream_channel.git
-      ref: null_safety
+    git: git://github.com/dart-lang/stream_channel.git
   string_scanner:
-    git:
-      url: git://github.com/dart-lang/string_scanner.git
-      ref: null_safety
+    git: git://github.com/dart-lang/string_scanner.git
   term_glyph:
-    git:
-      url: git://github.com/dart-lang/term_glyph.git
-      ref: null_safety
+    git: git://github.com/dart-lang/term_glyph.git
   test_api:
     git:
       url: git://github.com/dart-lang/test.git
-      ref: null_safety
       path: pkgs/test_api
   test_core:
     git:
       url: git://github.com/dart-lang/test.git
-      ref: null_safety
       path: pkgs/test_core
   test:
     git:
       url: git://github.com/dart-lang/test.git
-      ref: null_safety
       path: pkgs/test
+  typed_data: 1.3.0-nullsafety