Rack::Lock undefined for threadsafe Rails apps

[teamon]

When using config.threadsafe! there is no Rack::Lock middleware, so

config.middleware.insert_before(Rack::Lock, Rack::LiveReload)

will not work.

I'd suggest using

config.middleware.insert_after(ActionDispatch::Static, Rack::LiveReload)

instead - works for both cases.

[teamon]

Please see #16