Undefined method `reload_path'

#1

I’m using the extension middleman-portfolio and during build I get the following error

/Users/paul/.rvm/gems/ruby-2.3.1/gems/middleman-portfolio-1.0.1/lib/middleman-portfolio.rb:98:in `register_extension_templates': undefined method `reload_path' for #<Middleman::Sources:0x007fe16ba661a8> (NoMethodError)

Looking at the Portfolio class (middleman-portfolio.rb), it inherits ::Middleman::Extension and calls the reload_path method in a class method:

def register_extension_templates
    # We call reload_path to register the templates directory with Middleman.
    # The path given to app.files must be relative to the Middleman site's root.
    templates_dir_relative_from_root = Pathname(TEMPLATES_DIR).relative_path_from(Pathname(app.root))
    app.files.reload_path(templates_dir_relative_from_root)
end

Is ::Middleman::CoreExtensions not inherited with ::Middleman::Extension?