Fix Button[icon] vertical align issue

close #12972

test codesandbox url: https://codesandbox.io/s/2p8k935jjp

components/button/style/mixin.less

@@ -118,7 +118,6 @@
   > .@{btnClassName},
   > span > .@{btnClassName} {
     position: relative;
-    line-height: @btn-height-base - 2px;
 
     &:hover,
     &:focus,
@@ -168,6 +167,7 @@
 
   > .@{iconfont-css-prefix} {
     line-height: 1;
+    vertical-align: -0.19em;
   }
 
   &,