update with-asset-import example (#4830)

Changes:
- use `next-images` plugin for handling static files import

examples/with-asset-imports/.babelrc

-{
-  "presets": ["next/babel"],
-  "plugins": [
-    [
-      "transform-assets-import-to-string",
-      {
-        "baseDir": "static",
-        "baseUri": "/"
-      }
-    ]
-  ]
-}

examples/with-asset-imports/next.config.js

+const withImages = require('next-images')
+module.exports = withImages()

examples/with-asset-imports/package.json

@@ -7,8 +7,8 @@
     "start": "next start"
   },
   "dependencies": {
-    "babel-plugin-transform-assets-import-to-string": "^1.0.1",
     "next": "latest",
+    "next-images": "0.10.5",
     "react": "^16.0.0",
     "react-dom": "^16.0.0"
   },