Fix layout issue on plugin container

Summary: Reverted a change in D30192002 (9e5575cf69) that unintendendly caused some plugin containers to grow too big.

Reviewed By: nikoant

Differential Revision: D31609023

fbshipit-source-id: 56daa5efe6d9071a856536a59b473f17796201eb

desktop/app/src/sandy-chrome/SandyApp.tsx

@@ -138,7 +138,7 @@ export function SandyApp() {
   ) : null;
 
   return (
-    <Layout.Container grow>
+    <Layout.Bottom>
       <Layout.Left>
         <Layout.Horizontal>
           <LeftRail
@@ -179,7 +179,7 @@ export function SandyApp() {
         </MainContainer>
       </Layout.Left>
       <_PortalsManager />
-    </Layout.Container>
+    </Layout.Bottom>
   );
 }