Better docker for the frontend (#240)

* Exclude vscode local settings

* Switch the image to nginx with ENV support

* Add some doc

* Fix travis config

* Ignore coverage data

* Remove version labels

* Fix the Dockerfile according to the recent refactoring

* Cleanup

* Change maintainer

According to @woss request

* Fix travis config

frontend/public/index.html

@@ -6,6 +6,7 @@
     <meta name="theme-color" content="#000000">
     <!-- <link rel="manifest" href="%PUBLIC_URL%/manifest.json"> -->
     <title>Polkadot Telemetry</title>
+    <script type="text/javascript" src="/env-config.js"></script>
     <style>
       body, html {
         background: #fff;