docs(select): add missing id attributes in examples

Author: gkalpak

src/ng/directive/select.js

@@ -166,7 +166,7 @@ var SelectController =
  *     </select><br>
  *
  *     <label for="singleSelect"> Single select with "not selected" option and dynamic option values: </label><br>
- *     <select name="singleSelect" ng-model="data.singleSelect">
+ *     <select name="singleSelect" id="singleSelect" ng-model="data.singleSelect">
  *       <option value="">---Please select---</option> <!-- not selected / blank option -->
  *       <option value="{{data.option1}}">Option 1</option> <!-- interpolation -->
  *       <option value="option-2">Option 2</option>
@@ -207,7 +207,7 @@ var SelectController =
  * <div ng-controller="ExampleController">
  *   <form name="myForm">
  *     <label for="repeatSelect"> Repeat select: </label>
- *     <select name="repeatSelect" ng-model="data.repeatSelect">
+ *     <select name="repeatSelect" id="repeatSelect" ng-model="data.repeatSelect">
  *       <option ng-repeat="option in data.availableOptions" value="{{option.id}}">{{option.name}}</option>
  *     </select>
  *   </form>