rm margins of footer to correct its position

assets/css/page.less

@@ -50,8 +50,6 @@
     position: absolute;
     bottom: 0;
     margin: 0;
-    margin-top: @footer-height;
-    margin-bottom: @page-margin-bottom;
     width: 100%;
     height: @footer-height;
     text-align: center;