Update SDK version used by Travis.
diff --git a/.travis.yml b/.travis.yml
index 93d3428..04de0b4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
 language: dart
 
 dart:
-  - 2.3.0
+  - stable
   - dev
 
 dart_task: