remove deprecated property in KeyboardEvent

src/reducers/input.js

@@ -1,23 +1,18 @@
 import actions from '../actions';
 
 const defaultState = {
-  keys: [],
+  keys: '',
 };
 
 export default function reducer(state = defaultState, action = {}) {
   switch (action.type) {
   case actions.INPUT_KEY_PRESS:
     return Object.assign({}, state, {
-      keys: state.keys.concat([
-        {
-          code: action.code,
-          ctrl: action.ctrl
-        }
-      ])
+      keys: state.keys + action.key
     });
   case actions.INPUT_CLEAR_KEYS:
     return Object.assign({}, state, {
-      keys: [],
+      keys: '',
     });
   default:
     return state;