Change improper role attr of drag drop submission form.

Author: afrisalyp

src/shared/components/SubmissionPage/FilestackFilePicker/index.jsx

@@ -301,7 +301,7 @@ Uploading:
                 }).then(file => this.onSuccess(file, path));
                 return undefined;
               }}
-              role="button"
+              role="tab"
               styleName="drop-zone-mask"
               tabIndex={0}
             />