CI: Test on dev branch (#19)

diff --git a/.travis.yml b/.travis.yml
index e1bd731..19bd416 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
 language: dart
 
 dart:
-- preview/raw/2.10.0-0.2-dev
+- dev
 
 dart_task:
   - test: -p vm,chrome