Allow use of the fallback loading solution (#473)

LoadError does not descend from `StandardError` so the fallback loading is never invoked.
```
>> LoadError.ancestors
=> [LoadError, ScriptError, Exception, Object, Kernel, BasicObject]
```

Author: pboling

lib/annotate/annotate_models.rb

@@ -613,7 +613,7 @@ def get_model_class(file)
     # Retrieve loaded model class by path to the file where it's supposed to be defined.
     def get_loaded_model(model_path)
       ActiveSupport::Inflector.constantize(ActiveSupport::Inflector.camelize(model_path))
-    rescue
+    rescue StandardError, LoadError
       # Revert to the old way but it is not really robust
       ObjectSpace.each_object(::Class)
                  .select do |c|