Serve underscore in karma tests

Because of the way that we're using underscore in the ES bundle (using the
global), we need to include underscore globally

services/web/karma.conf.js

@@ -18,6 +18,7 @@ module.exports = function (config) {
       'public/js/libs/angular-1.6.4.min.js',
       'public/js/libs/angular-mocks.js',
       'public/js/libs/jquery-1.11.1.min.js',
+      'public/js/libs/underscore-1.3.3.js',
       // Set up requirejs
       'test/unit_frontend/js/test-main.js',
       // Include source & test files, but don't "include" them as requirejs