use ng-bind-html for scope variable injection

I have a custom AngularJs template tags (`{$ $}`) in my project so the injection of the scope variable `ngNotify.notifyMessage` do not work. This also prevent rendering `html` in the notification message.

line 64 in `ng-notify.js`:

    var tpl = $compile(
                    '<div class="ngn" ng-class="ngNotify.notifyClass">' +
                        '<span class="ngn-dismiss" ng-click="dismiss()">&times;</span>' +
                        '<span>{{ ngNotify.notifyMessage  }}</span>' +
                    '</div>'
                )(notifyScope);

I suggest it should be this way rather.

    var tpl = $compile(
                    '<div class="ngn" ng-class="ngNotify.notifyClass">' +
                        '<span class="ngn-dismiss" ng-click="dismiss()">&times;</span>' +
                        '<span ng-bind-html="ngNotify.notifyMessage"></span>' +
                    '</div>'
                )(notifyScope);

This will prevent conflict with other templating language.