allow the 2.12 prerelease sdks and prep for release (#29)

* allow the 2.12 prerelease sdks

* require null safe deps
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ed62ea..602add9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.1.0-nullsafety.2
+
+* Allow prerelease versions of the 2.12 sdk.
+
 ## 2.1.0-nullsafety.1
 
 * Allow 2.10 stable and 2.11.0 dev SDK versions.
diff --git a/pubspec.yaml b/pubspec.yaml
index c32b86f..1ec3af7 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: boolean_selector
-version: 2.1.0-nullsafety.1
+version: 2.1.0-nullsafety.2
 description: >-
   A flexible syntax for boolean expressions, based on a simplified version of
   Dart's expression syntax.
@@ -7,68 +7,14 @@
 
 environment:
   # This must remain a tight constraint until nnbd is stable
-  sdk: '>=2.10.0-0 <2.11.0'
+  sdk: '>=2.10.0-0 <2.12.0'
 
 dependencies:
   source_span: '>=1.8.0-nullsafety <1.8.0'
   string_scanner: '>=1.1.0-nullsafety <1.1.0'
 
 dev_dependencies:
-  pedantic: ^1.0.0
-  test: any
-  test_api: any
-  test_core: any
-
-dependency_overrides:
-  async:
-    git: git://github.com/dart-lang/async.git
-  charcode:
-    git: git://github.com/dart-lang/charcode.git
-  collection:
-    git: git://github.com/dart-lang/collection.git
-  js:
-    git:
-      url: git://github.com/dart-lang/sdk.git
-      path: pkg/js
-      ref: 2-10-pkgs
-  matcher:
-    git: git://github.com/dart-lang/matcher.git
-  meta:
-    git:
-      url: git://github.com/dart-lang/sdk.git
-      path: pkg/meta
-      ref: 2-10-pkgs
-  path:
-    git: git://github.com/dart-lang/path.git
-  pedantic:
-    git: git://github.com/dart-lang/pedantic.git
-  pool:
-    git: git://github.com/dart-lang/pool.git
-  source_maps:
-    git: git://github.com/dart-lang/source_maps.git
-  source_map_stack_trace:
-    git: git://github.com/dart-lang/source_map_stack_trace.git
-  source_span:
-    git: git://github.com/dart-lang/source_span.git
-  stack_trace:
-    git: git://github.com/dart-lang/stack_trace.git
-  stream_channel:
-    git: git://github.com/dart-lang/stream_channel.git
-  string_scanner:
-    git: git://github.com/dart-lang/string_scanner.git
-  term_glyph:
-    git: git://github.com/dart-lang/term_glyph.git
-  test_api:
-    git:
-      url: git://github.com/dart-lang/test.git
-      path: pkgs/test_api
-  test_core:
-    git:
-      url: git://github.com/dart-lang/test.git
-      path: pkgs/test_core
-  test:
-    git:
-      url: git://github.com/dart-lang/test.git
-      path: pkgs/test
-  typed_data:
-    git: git://github.com/dart-lang/typed_data.git
+  pedantic: ^1.10.0-nullsafety
+  test: ^1.16.0-nullsafety
+  test_api: ^0.2.19-nullsafety
+  test_core: ^0.3.12-nullsafety