Configured all Admin assets to contain fingerprint hash

refs https://github.com/TryGhost/Toolbox/issues/403

- as we're moving towards independent Admin releases, we want to make
  sure that we can bust cache when an asset is updated
- right now, svg, ttf and ico images aren't fingerprinted, so if they
  change, it'll require a browser cache clear to update them
- instead, we should add them to the list of fingerprinted file
  extensions to fix this issue

ghost/admin/ember-cli-build.js

@@ -135,7 +135,7 @@ module.exports = function (defaults) {
         },
         fingerprint: {
             enabled: isProduction,
-            extensions: ['js', 'css', 'png', 'jpg', 'jpeg', 'gif', 'map']
+            extensions: ['js', 'css', 'png', 'jpg', 'jpeg', 'gif', 'map', 'svg', 'ttf', 'ico']
         },
         minifyJS: {
             options: {