fix: inset compatibility (#345)

Author: yuuk

assets/index.less

@@ -3,22 +3,29 @@
 @prefixCls: rc-drawer;
 @zIndex: 1050;
 
+.inset-0() {
+  top: 0;
+  bottom: 0;
+  left: 0;
+  right: 0;
+}
+
 .@{prefixCls} {
+  .inset-0;
   position: fixed;
   z-index: @zIndex;
   pointer-events: none;
-  inset: 0;
 
   &-inline {
     position: absolute;
   }
 
   &-mask {
+    .inset-0;
     position: absolute;
     z-index: @zIndex;
     background: rgba(0, 0, 0, 0.5);
     pointer-events: auto;
-    inset: 0;
   }
 
   &-content-wrapper {