Fix column sorting not visible

Summary: Fixes a regression from D45394048. It "sortable" as a nullable column prop. When it is undefined it should be treated as true.

Reviewed By: LukeDefeo

Differential Revision: D45776216

fbshipit-source-id: dcd8ce97217086deab7b2b1852837fbfa7437d13

desktop/flipper-plugin/src/ui/data-table/TableHead.tsx

@@ -175,7 +175,7 @@ function TableHeadColumn({
   };
 
   let divProps: HTMLAttributes<HTMLDivElement> = {};
-  if (column.sortable) {
+  if (column.sortable !== false) {
     divProps = {
       onClick: (e) => {
         e.stopPropagation();
@@ -208,7 +208,7 @@ function TableHeadColumn({
           ) : (
             column.title
           )}
-          {column.sortable ? (
+          {column.sortable !== false ? (
             <SortIcons
               direction={sorted}
               onSort={(dir) =>