fix offset in login page

src/client/styles/scss/_login.scss

@@ -225,7 +225,7 @@
 .nologin.error {
   .main .row {
     @media (min-width: 510px) {
-      .col-sm-offset-4 {
+      .offset-sm-4 {
         margin-left: calc(50% - 240px);
       }
 

src/server/views/login/error.html

@@ -26,7 +26,7 @@
 
   <div class="row">
 
-    <div class="login-header col-sm-offset-4 col-sm-4">
+    <div class="login-header offset-sm-4 col-sm-4">
       <div class="logo">{% include '../widget/logo.html' %}</div>
       <h1>GROWI</h1>