Test on oldest supported Dart SDK (2.0.0)

pkgs/test_descriptor/.travis.yml

diff --git a/pkgs/test_descriptor/.travis.yml b/pkgs/test_descriptor/.travis.yml
index 48803a1..3fa092b 100644
--- a/pkgs/test_descriptor/.travis.yml
+++ b/pkgs/test_descriptor/.travis.yml
@@ -2,7 +2,7 @@
 
 dart:
   - dev
-  - stable
+  - 2.1.0
 
 dart_task:
   - test
@@ -14,7 +14,7 @@
   - dart: dev
     dart_task:
       dartanalyzer: --fatal-infos --fatal-warnings .
-  - dart: stable
+  - dart: 2.1.0
     dart_task:
       dartanalyzer: --fatal-warnings .
 

pkgs/test_descriptor/pubspec.yaml

diff --git a/pkgs/test_descriptor/pubspec.yaml b/pkgs/test_descriptor/pubspec.yaml
index b50a18b..e268ab5 100644
--- a/pkgs/test_descriptor/pubspec.yaml
+++ b/pkgs/test_descriptor/pubspec.yaml
@@ -5,7 +5,7 @@
 homepage: https://github.com/dart-lang/test_descriptor
 
 environment:
-  sdk: '>=2.0.0 <3.0.0'
+  sdk: '>=2.1.0 <3.0.0'
 
 dependencies:
   archive: '^2.0.0'