change submission button req to better reflect action

spec/features/position_features_spec.rb

@@ -113,7 +113,7 @@
       visit user_position_management_path(user.id)
 
       page.check(position2.name)
-      click_button("Update User")
+      click_button("Manage Position(s)")
 
       expect(user.positions).to include(position1, position2)
     end