CI: Only push binaries for develop branch builds

... for now.
Syntax was confusing Travis CI, AppVeyor is reporting 401,
so lets see if this change at least fixes Travis.

If this doesn't work, it might be that @raysan5's token is required.

.travis.yml

@@ -54,6 +54,4 @@ deploy:
   skip_cleanup: true
   on:
     repo: raysan5/raylib
-    branch:
-      - develop
-      - master
+    branch: develop