test on oldest supported SDK

pkgs/yaml/.travis.yml

diff --git a/pkgs/yaml/.travis.yml b/pkgs/yaml/.travis.yml
index 6105af8..63ec5c2 100644
--- a/pkgs/yaml/.travis.yml
+++ b/pkgs/yaml/.travis.yml
@@ -1,12 +1,14 @@
 language: dart
 
 dart:
+  - 2.0.0
   - dev
+
 dart_task:
   - test: -p vm
     xvfb: false
   - test: -p firefox
-  - dartanalyzer
+  - dartanalyzer: --fatal-warnings --fatal-infos .
 
 matrix:
   include:

pkgs/yaml/pubspec.yaml

diff --git a/pkgs/yaml/pubspec.yaml b/pkgs/yaml/pubspec.yaml
index e42ab42..da41f3a 100644
--- a/pkgs/yaml/pubspec.yaml
+++ b/pkgs/yaml/pubspec.yaml
@@ -6,7 +6,7 @@
 homepage: https://github.com/dart-lang/yaml
 
 environment:
-  sdk: '>=2.0.0-dev.49.0 <3.0.0'
+  sdk: '>=2.0.0 <3.0.0'
   
 dependencies:
   charcode: ^1.1.0