Update travis to run only on dev, pub get fails on stable
diff --git a/.travis.yml b/.travis.yml
index 662d2fe..8d63d09 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,9 +2,6 @@
 sudo: false
 dart:
   - dev
-  - stable
-  - 1.23.0
-  - 1.22.1
 cache:
   directories:
     - $HOME/.pub-cache