Bump version of CSS files to invalidate browser cache

Author: benfrancis

gateway/index.html

@@ -7,9 +7,9 @@
   <link rel="canonical" href="https://webthings.io/gateway">
   <link rel="icon" href="/images/icon.svg" />
   <link rel="stylesheet" type="text/css" href="/css/site.css" />
-  <link rel="stylesheet" type="text/css" href="css/gateway.css" />
+  <link rel="stylesheet" type="text/css" href="css/gateway.css?v=2 />
   <link rel="stylesheet" media="(max-width: 959px)" href="/css/site-mobile.css" />
-  <link rel="stylesheet" media="(max-width: 959px)" href="css/gateway-mobile.css" />
+  <link rel="stylesheet" media="(max-width: 959px)" href="css/gateway-mobile.css?v=2" />
   <meta name="description" content="Build your own Web of Things gateway" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:site" content="@WebThingsIO" />