Prepare to publish for stable null safety (#112)

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25b209e..d85405d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 3.0.0
+
+* Stable release for null safety.
 
 ## 3.0.0-nullsafety.0
 

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 4e0ab56..1beeaae 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: crypto
-version: 3.0.0-nullsafety.0
+version: 3.0.0
 description: Implementations of SHA, MD5, and HMAC cryptographic functions
 homepage: https://www.github.com/dart-lang/crypto
 
@@ -7,17 +7,9 @@
   sdk: '>=2.12.0-0 <3.0.0'
 
 dependencies:
-  collection: ^1.15.0-nullsafety
-  typed_data: ^1.3.0-nullsafety
+  collection: ^1.15.0
+  typed_data: ^1.3.0
 
 dev_dependencies:
   pedantic: ^1.10.0-nullsafety
   test: ^1.16.0-nullsafety
-
-dependency_overrides:
-  analyzer: ^0.41.0
-  test: ^1.16.0-nullsafety.12
-  test_api: ^0.2.19-nullsafety.6
-  test_core: ^0.3.12-nullsafety.11
-  web_socket_channel:
-    git: git://github.com/dart-lang/web_socket_channel.git