//= require jquery.autoresize.js
I'm assuming we're talking about the production environment.
rake assets:precompile; this task compiles and compresses the various .js and .css files and creates the application.js and application.css files that is loaded by your views.
It's possible that if you replaced
jquery.autoresize.js with a version with an older timestamp, the precompile step might skip it, thinking the compiled version is up-to-date. You can avoid that by running
rake assets:clean first, forcing it to rebuild everything in the
public/assets directory from scratch.