Issue when add the canenter feature. #259

In some cases when using the canenter when validate the step, some times y show this error:

ReferenceError
columnNumber: 82
fileName: "http://localhost:8000/node_modules/angular-wizard/dist/angular-wizard.js"
lineNumber: 236
message: "_ is not defined"

i resolve change this line of code
//original
//$scope.$emit('wizard:stepChangeFailed', {step: step, index: _.indexOf($scope.getEnabledSteps(), step)});
//changed
$scope.$emit('wizard:stepChangeFailed', {step: step, index:stepIdx(step)});

in other issues it mentioned the dependency of lodash.underscore, maybe this line correspond on that changed that doesnt update. Hope this helps.