Fixed variable in Readme

The example created one object, but in the next line it referred to a different configuration object.

```js
myAppModule.controller('MyController', function($scope) {
    /* config object */
    $scope.uiConfig = {
      calendar:{
...
      }
    };
});

<div ui-calendar="calendarOptions" ng-model="eventSources">
```

to
```js
<div ui-calendar="uiConfig.calendar" ng-model="eventSources">
```