Quote branch name to make it a string [ci skip]
diff --git a/.travis.yml b/.travis.yml
index a170fb8..7af8041 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,7 @@
 branches:
   only:
     - master
-    - 2.3
+    - "2.3"
 
 env:
   global: