修复BUG，Fix模式下弹出overlay出现滚动条

Bootstrap.Admin/Content/css/admin.css

@@ -21,6 +21,7 @@
     background: #2a3542;
     overflow-y: scroll;
     position: absolute;
+    padding-bottom: 15px;
 }
 
     #sidebar .sub-menu > .sub li {

Bootstrap.Admin/Content/css/site-responsive.css

@@ -40,8 +40,9 @@
         overflow: hidden;
         overflow-y: auto;
         position: absolute;
-        z-index: 1001;
+        z-index: 1;
         display: block;
+        padding-bottom: inherit;
     }
 
     #sidebar {
@@ -95,7 +96,7 @@
     }
 
     #sidebar {
-        margin-top: 94px;
+        padding-top: 94px;
         height: 100%;
     }