fix: don't use public path when determining as value (vuejs#11)

Fixes vuejs/vue-cli#5672

Author: Tofandel

src/index.js

@@ -75,7 +75,7 @@ class PreloadPlugin {
       // then we need to set the 'as' attribute correctly.
       if (options.rel === 'preload') {
         attributes.as = determineAsValue({
-          href,
+          href: file,
           optionsAs: options.as
         })