typeahead numeric sources (ie. years)
typeahead numeric sources (ie. years)

When numeric sources an error was thrown:

```javascript
    private years: Array<any> = [];
    private getYears() {
        if ((this.years.lenght >>> 0) === 0) {
            for (var i = yearNow; i >= minYear; i -= 1) {
                var yearNow = new Date().getFullYear() - 16,
                    minYear = yearNow - 100;

                this.years.push({
                    id: i,
                    description: i
                });
            }
        }
        return this.years;
    }
```

```html
<input [typeahead]="getYears()" (typeahead-on-select)="onSelectYear($event)" [typeahead-option-field]="'id'" [placeholder]="'Year'">
```


```
TypeError: match.toLowerCase is not a function
    at Typeahead.processMatches (http://127.0.0.1:8080/public/node_modules/ng2-bootstrap/components/typeahead/typeahead.js:182:27)
    at Typeahead.onChange (http://127.0.0.1:8080/public/node_modules/ng2-bootstrap/components/typeahead/typeahead.js:272:18)
    at AbstractChangeDetector.ChangeDetector_TypeaheadDiba_0.handleEventInternal (eval at <anonymous> (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:22300:14), <anonymous>:384:36)
    at AbstractChangeDetector.handleEvent (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:22051:22)
    at AppView.dispatchEvent (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:18939:39)
    at AppView.dispatchRenderEvent (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:18934:19)
    at DefaultRenderView.dispatchRenderEvent (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:14785:53)
    at eventDispatcher (http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:19876:19)
    at http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:19947:14
    at http://127.0.0.1:8080/node_modules/angular2/bundles/angular2.dev.js:28650:34
```
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