fix: only deploy demo app from master branch, and only from build leader

.travis.yml

@@ -54,11 +54,10 @@ after_success:
 # Generate the github pages. When this command is finished I'll be on "master" branch with a
 # new commit already made (but not pushed)
 # Push the new commit
-- /bin/bash lib/try-generate-pages.sh
+- yarn travis-deploy-once /bin/bash lib/try-generate-pages.sh
 - git checkout master
 
 
-
 stages:
   - basic test
   - additional tests