💄 tweak tree switcher icon size

components/tree/style/mixin.less

@@ -6,7 +6,7 @@
 .antTreeSwitcherIcon(@type: "tree-default-open-icon") {
   .@{tree-prefix-cls}-switcher-icon,
   .@{tree-select-prefix-cls}-switcher-icon {
-    .iconfont-size-under-12px(7px);
+    .iconfont-size-under-12px(10px);
     display: inline-block;
     font-weight: bold;
     svg {
@@ -18,7 +18,7 @@
 .antTreeShowLineIcon(@type) {
   .@{tree-prefix-cls}-switcher-icon,
   .@{tree-select-prefix-cls}-switcher-icon {
-    .iconfont-size-under-12px(12px);
+    font-size: 12px;
     display: inline-block;
     font-weight: normal;
     svg {