adjust style for header

lib/views/crowi-plus/widget/header.html

@@ -1,7 +1,7 @@
 <div class="header-wrap">
   <header id="page-header">
     <div class="flex-title-line">
-      <div class="title-logo-container visible-lg visible-md">
+      <div class="title-logo-container hidden-xs hidden-sm">
         <a href="/">
           <img alt="Crowi" src="/logo/32x32_g.png" />
         </a>