fix(TranslateDirective): support ng2-translate attribute (for protractor)

Protractor treats `translate` as a boolean because it is an html5 attribute, use `ng2-translate` instead if this is a problem for you

Author: ocombe

src/translate.directive.ts

@@ -4,7 +4,7 @@ import {isDefined} from "./util";
 import {TranslateService, LangChangeEvent} from "./translate.service";
 
 @Directive({
-    selector: '[translate]'
+    selector: '[translate],[ng2-translate]'
 })
 export class TranslateDirective implements AfterViewChecked, OnDestroy {
     key: string;