fix(ionRadio): correctly interpolate ngValue instead of compiling

Closes #1464

demos/directive/radio/chooseOne/index.html

@@ -0,0 +1,17 @@
+---
+name: chooseOne
+component: ionRadio
+---
+<ion-header-bar class="bar-positive">
+  <h1 class="title">Radios</h1>
+</ion-header-bar>
+<ion-content ng-controller="ChooseOneCtrl">
+  <h1>
+    Your Choice: <span class="assertive">{{choice}}</span> 
+  </h1>
+  <ion-radio ng-model="choice" ng-value="one">One</ion-radio>
+  <ion-radio ng-model="choice" ng-value="two">Two</ion-radio>
+  <ion-radio ng-model="choice" ng-value="three">Three</ion-radio>
+  <ion-radio ng-model="choice" ng-value="four">Four</ion-radio>
+  <ion-radio ng-model="choice" ng-value="five">Five</ion-radio>
+</ion-content>

demos/directive/radio/chooseOne/index.js

@@ -0,0 +1,8 @@
+---
+name: chooseOne
+component: ionRadio
+---
+angular.module('chooseOne', ['ionic'])
+.controller('ChooseOneCtrl', function($scope) {
+  $scope.choice = 'two';
+});