title: typescript Cannot invoke an expression whose type lacks a call signature?
body: <p>I am calling <code>combineReducers</code> (<code>import { combineReducers } from 'redux-immutable'</code>) in <code>typescript</code> like this:</p>
  
  <pre><code>return combineReducers({
      byId,
      visibleIds
  })(state, action)
  </code></pre>
  
  <p>but typescript complains this:</p>
  
  <pre><code>Cannot invoke an expression whose type lacks a call signature.
  </code></pre>
  
  <p>so I see the type definition file:</p>
  
  <pre><code>declare module "redux-immutable" {
      export function combineReducers(reducers : Object): Object;
  }
  </code></pre>
  
  <p>how can I call <code>combineReducer</code> correctly?</p>