Fix display of brackets in the labels view

Fixes https://jira.coreos.com/browse/QUAY-983

static/js/directives/ui/label-view.js

@@ -24,7 +24,7 @@ angular.module('quay').directive('labelView', function () {
         bootbox.alert({
           size: "small",
           title: $scope.label.key,
-          message: '<pre>' + $sanitize($scope.label.value) + '</pre>'
+          message: '<pre>' + $sanitize($scope.label.value.replace('<', '&lt;').replace('>', '&gt;')) + '</pre>'
         });
       };
     }