Cache bust css for keras.io (#2073)

We should ideally do this through a fancier hosting solution rather
than this manual approach. But let's get this out to unbreak peoples
pages.

Author: mattdangerw

theme/base.html

@@ -30,7 +30,7 @@
   <link href="{{base_url}}css/bootstrap.min.css" rel="stylesheet">
 
   <!-- Custom styles for this template -->
-  <link href="{{base_url}}css/docs.css" rel="stylesheet">
+  <link href="{{base_url}}css/docs.css?v=2" rel="stylesheet">
   <link href="{{base_url}}css/monokai.css" rel="stylesheet">
 
   <!-- Google Tag Manager -->

theme/keras_3.html

@@ -18,8 +18,8 @@
   <link href="https://fonts.googleapis.com/css?family=Open+Sans:wght@300;400;500;600&display=swap" rel="stylesheet">
 
   <!-- Custom styles for this template -->
-  <link href="/css/landing.css" rel="stylesheet">
-  <link href="/css/announcement.css" rel="stylesheet">
+  <link href="/css/landing.css?v=2" rel="stylesheet">
+  <link href="/css/announcement.css?v=2" rel="stylesheet">
   <link href="{{base_url}}css/monokai.css" rel="stylesheet">
 
   <!-- Google Tag Manager -->

theme/landing.html

@@ -38,7 +38,7 @@
     />
 
     <!-- Custom styles for this template -->
-    <link href="css/landing.css" rel="stylesheet">
+    <link href="css/landing.css?v=2" rel="stylesheet">
 
     <!-- Google Tag Manager -->
     <script>