Fixed margin issue with box loding state

build/less/boxes.less

@@ -137,7 +137,7 @@
   > .overlay,
   > .loading-img {
     position: absolute;
-    top: -3px;
+    top: 0;
     left: 0;
     width: 100%;
     height: 100%;

dist/css/AdminLTE.css

@@ -1309,7 +1309,7 @@ a:focus {
 .box > .overlay,
 .box > .loading-img {
   position: absolute;
-  top: -3px;
+  top: 0;
   left: 0;
   width: 100%;
   height: 100%;