Prepare for stable release of null safety (#34)

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 08216dc..4465d51 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,6 @@
-## 1.1.0-nullsafety.4-dev
+## 1.1.0
+
+* Stable release for null safety.
 
 ## 1.1.0-nullsafety.3
 

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 0d29f2e..5ecd164 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: string_scanner
-version: 1.1.0-nullsafety.4-dev
+version: 1.1.0
 
 description: A class for parsing strings using a sequence of patterns.
 homepage: https://github.com/dart-lang/string_scanner
@@ -8,8 +8,8 @@
   sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
-  charcode: '>=1.2.0-nullsafety <1.2.0'
-  source_span: '>=1.8.0-nullsafety <1.8.0'
+  charcode: ^1.2.0
+  source_span: ^1.8.0
 
 dev_dependencies:
-  test: '>=1.16.0-nullsafety <1.16.0'
+  test: ^1.16.0-nullsafety