chore: set max SDK version to <3.0.0 upgrade test and remove browser … (flutter#7)

* adjust test package version constrain to support dart 1.23
* Remove 1.23.0 SDK from travis

Author: eredo

.travis.yml

@@ -3,7 +3,6 @@ language: dart
 dart:
   - dev
   - stable
-  - 1.23.0
 
 dart_task:
   - test

example/index.dart

@@ -5,7 +5,7 @@ void main() {
   var span = querySelector('#count') as SpanElement;
 
   HttpRequest.getString('/api').then((value) {
-    return JSON.decode(value);
+    return json.decode(value);
   }).then((obj) {
     var count = obj['count'];
     span.text = count.toString();

pubspec.yaml

@@ -4,11 +4,10 @@ author: Dart Team <misc@dartlang.org>
 description: A shelf handler for proxying requests to another server.
 homepage: https://github.com/dart-lang/shelf_proxy
 environment:
-  sdk: '>=1.23.0 <2.0.0'
+  sdk: '>=2.0.0-dev <3.0.0'
 dependencies:
   http: '>=0.9.0 <0.12.0'
   path: '>=1.0.0 <2.0.0'
   shelf: '>=0.5.2 <0.8.0'
 dev_dependencies:
-  browser: '>=0.10.0 <0.11.0'
-  test: '>=0.12.0 <0.13.0'
+  test: ^1.3.0