Fix collapse animation

style/components/collapse.less

@@ -50,7 +50,7 @@
   }
 
   &-content {
-    height: 0;
+    display: none;
     overflow: hidden;
     color: @text-color;
     padding: 0 16px;
@@ -60,6 +60,10 @@
       padding-top: 16px;
       padding-bottom: 16px;
     }
+
+    &-active {
+      display: block;
+    }
   }
 
   &-collapsing {
@@ -73,10 +77,6 @@
     }
   }
 
-  &-content-active {
-    height: auto;
-  }
-
   & > &-item-active {
     > .@{collapse-prefix-cls}-header {