Travis: Update min tested SDK
diff --git a/.travis.yml b/.travis.yml
index 416dd71..376cd50 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@
     fi
 
 dart:
-  - 2.2.0
+  - 2.5.0-dev.0.0
   - dev
 
 dart_task: