mime: update .mjs MIME type from text/ to application/javascript
mime: update .mjs MIME type from text/ to application/javascript

.mjs should be the same MIME type as .js, and RFC 4329 says that
text/javascript is obsolete, even back in 2006:

    https://tools.ietf.org/html/rfc4329#section-7.1

I didn't notice this when I recently reviewed CL 169502.

Also, re-sort it.

Updates #30547

Change-Id: I8ed8ddaf06c8a08b010423ebd071f39ef3a325e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/175459
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
Run-TryBot: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,akutz/go,CAFxX/go,golang/go,CAFxX/go,golang/go,cloudflare/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,akutz/go,CAFxX/go,nawawi/go,nawawi/go,nawawi/go,cloudflare/go,nawawi/go,CAFxX/go,akutz/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,golang/go,golang/go