small clean-ups; sdk version constraint (#13)

Author: yjbanov

.travis.yml

@@ -1,5 +1,5 @@
 language: dart
 dart:
-  - stable
+  # - stable # there's no Dart 2 on the stable channel yet
   - dev
 script: ./tool/presubmit.sh

README.md

@@ -7,9 +7,9 @@ program to https://sentry.io error tracking service.
 
 ## Versions
 
->=0.0.0 and <2.0.0 is the range of versions compatible with Dart 1.
+`>=0.0.0 <2.0.0` is the range of versions compatible with Dart 1.
 
->=2.0.0 and <3.0.0 is the range of versions compatible with Dart 2.
+`>=2.0.0 <3.0.0` is the range of versions compatible with Dart 2.
 
 ## Usage
 

pubspec.yaml

@@ -4,6 +4,9 @@ description: A pure Dart Sentry.io client.
 author: Flutter Authors <[email protected]>
 homepage: https://github.com/flutter/sentry
 
+environment:
+  sdk: ">=2.0.0-dev.28.0 <3.0.0"
+
 dependencies:
   http: ">=0.11.0 <2.0.0"
   meta: ">=1.0.0 <2.0.0"