fix: update upload preview button styles (#36)

Author: zacheryconverse

src/styles/vendor/react-file-utils.scss

@@ -139,6 +139,8 @@
   -webkit-box-pack: center;
   -ms-flex-pack: center;
   justify-content: center;
+  border: none;
+  background: transparent;
 }
 .rfu-icon-button svg {
   margin: 4px;