Allow zoom on mobile devices

See https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#user-scalable

template/templates/common/layout.html

@@ -6,7 +6,7 @@
     <title>{{template "title" .}} - Miniflux</title>
 
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
-    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <meta name="mobile-web-app-capable" content="yes">
     <meta name="apple-mobile-web-app-title" content="Miniflux">
     <link rel="manifest" href="{{ route "webManifest" }}" crossorigin="use-credentials"/>