Add overflow suppression to custom file label

Avoids unsightly spilling out of long filename text, particularly for multi file inputs

scss/_custom-forms.scss

@@ -348,6 +348,7 @@
   z-index: 1;
   height: $custom-file-height;
   padding: $custom-file-padding-y $custom-file-padding-x;
+  overflow: hidden;
   font-family: $custom-file-font-family;
   font-weight: $custom-file-font-weight;
   line-height: $custom-file-line-height;