remove unknown rollup input option breakOnWarning

As seen in https://buildkite.com/rails/rails/builds/104749#018d92dc-79b9-42bc-9a8c-bbcf5681f9eb/1165-1176 breakOnWarning does not seem to be a valid option for Rollup. I cannot find in the documentation, and therefore I think it can safely be removed.

Author: hendrixfan

actioncable/rollup.config.js

@@ -38,10 +38,9 @@ export default [
       format: "umd",
       name: "ActionCable"
     },
-    breakOnWarning: false,
     plugins: [
       resolve(),
       terser(terserOptions)
     ]
   },
-]
+]