Fix modal flex issue in IE11

src/definitions/modules/modal.less

@@ -32,6 +32,8 @@
   box-shadow: @boxShadow;
   transform-origin: @transformOrigin;
 
+  flex: 0 0 auto;
+
   border-radius: @borderRadius;
   user-select: text;
   will-change: top, left, margin, transform, opacity;