Test analysis on oldest supported SDK (dart-lang/pubspec_parse#41)

pkgs/pubspec_parse/.travis.yml

diff --git a/pkgs/pubspec_parse/.travis.yml b/pkgs/pubspec_parse/.travis.yml
index 3af3939..b82f2f3 100644
--- a/pkgs/pubspec_parse/.travis.yml
+++ b/pkgs/pubspec_parse/.travis.yml
@@ -2,7 +2,6 @@
 
 dart:
   - dev
-  - stable
 
 dart_task:
   - test: -x presubmit-only
@@ -14,7 +13,7 @@
     - dart: dev
       dart_task:
         dartanalyzer: --fatal-infos --fatal-warnings .
-    - dart: stable
+    - dart: 2.0.0
       dart_task:
         dartanalyzer: --fatal-warnings .