Prevent expanded paths from getting into the history cache

Currently dependencies are mutated after they're pulled out of the cache. These same dependencies can then be re-stored later

```
cache.set(key, history.unshift(deps).take(limit))
```

This makes it possible for a project to load the wrong asset.

lib/sprockets/loader.rb

@@ -308,8 +308,10 @@ def fetch_asset_from_dependency_cache(unloaded, limit = 3)
 
         history = cache.get(key) || []
         history.each_with_index do |deps, index|
-          deps.map! { |path| path.start_with?("file-digest://") ? expand_from_root(path) : path }
-          if asset = yield(deps)
+          expanded_deps = deps.map do |path|
+            path.start_with?("file-digest://") ? expand_from_root(path) : path
+          end
+          if asset = yield(expanded_deps)
             cache.set(key, history.rotate!(index)) if index > 0
             return asset
           end