inject_styles.js is not preloaded in v0.28.8 when site exported

[TheComputerM]

As stated in this PR, inject_styles.js is said to be preloaded but when run lighthouse on svelte-materialify running sapper v0.28.8, is says:

[benmccann]

I do see inject_styles being preloaded on the HN sample site. I don't see any scripts being preloaded on your site though. I'm guessing this is a site you host via export? If so, then this was actually just fixed today in #1539 and will be part of the next release