enable to scroll the setting's page sidebar (#1347)

* enable to scroll the setting's page sidebar

add scroll:auto and use margin instead of padding for the bottom

* Update admin.scss

* Update admin.scss

* Update admin.scss

app/assets/stylesheets/admin.scss

@@ -14,7 +14,8 @@
   .sidebar {
     width: 240px;
     height: 100%;
-    padding: 20px 0;
+    padding: 0;
+    overflow-y: auto;
     
     .logo {
       display: block;
@@ -27,6 +28,7 @@
       list-style: none;
       border-radius: 4px 0 0 4px;
       overflow: hidden;
+      margin-bottom: 20px;
 
       a {
         display: block;
@@ -55,6 +57,7 @@
       ul {
         background: darken($color1, 4%);
         border-radius: 0 0 0 4px;
+        margin: 0;
 
         a {
           border: 0;