mime: update type of .js and .mjs files to text/javascript

application/javascript is being deprecated per
https://datatracker.ietf.org/doc/draft-ietf-dispatch-javascript-mjs/

Specify a charset to be consistent with other text/* mime types.

Fixes #32351

Change-Id: I7300f6cfdbcf574103764991cb75172a252a3400
Reviewed-on: https://go-review.googlesource.com/c/go/+/186927
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

src/mime/type.go

@@ -63,8 +63,8 @@ var builtinTypesLower = map[string]string{
 	".html": "text/html; charset=utf-8",
 	".jpeg": "image/jpeg",
 	".jpg":  "image/jpeg",
-	".js":   "application/javascript",
-	".mjs":  "application/javascript",
+	".js":   "text/javascript; charset=utf-8",
+	".mjs":  "text/javascript; charset=utf-8",
 	".pdf":  "application/pdf",
 	".png":  "image/png",
 	".svg":  "image/svg+xml",