use .key/.value instead of _key/_value

Author: yyx990803

examples/todoApp/index.html

@@ -11,9 +11,9 @@
 
     <div id="app">
       <ul>
-        <li v-for="item in items" track-by="_key">
+        <li v-for="item in items" track-by=".key">
           {{ item.text }}
-          <span @click="removeTodo(item._key)">X</span>
+          <span @click="removeTodo(item['.key'])">X</span>
         </li>
       </ul>
       <form @submit.prevent="addTodo">

src/vuefire.js

@@ -30,8 +30,8 @@
     var value = snapshot.val()
     var res = value && typeof value === 'object'
       ? value
-      : { _value: value }
-    res._key = snapshot.key()
+      : { '.value': value }
+    res['.key'] = snapshot.key()
     return res
   }
 
@@ -44,7 +44,7 @@
    */
   function indexForKey (array, key) {
     for (var i = 0; i < array.length; i++) {
-      if (array[i]._key === key) {
+      if (array[i]['.key'] === key) {
         return i
       }
     }