polyfills

app/template.html

@@ -11,6 +11,11 @@
 	<link rel='manifest' href='manifest.json'>
 	<link rel='icon' type='image/png' href='favicon.png'>
 
+	<script>
+		(window.Promise && [].includes && Object.assign && window.Map) ||
+		document.write('<script src="https://cdn.polyfill.io/v2/polyfill.min.js"><\/script>');
+	</script>
+
 	<!-- Sapper generates a <style> tag containing critical CSS
 	     for the current page. CSS for the rest of the app is
 	     lazily loaded when it precaches secondary pages -->