Drop dev (#524)

diff --git a/.travis.yml b/.travis.yml
index 20cee45..ac2723b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,6 @@
   # Keep this value aligned with min SDK value in pubspec.yaml and FROM line of Dockerfile
   - "2.7.2"
   - beta
-  - dev
 
 # Speed up builds by using containerization. Disable this if you need to use
 # sudo in your scripts.