fix: scope error inside `generateHref` function when using `slugify` modifier

[loga4]

Error:

Uncaught TypeError: Cannot read property 'helper' of undefined
    at jquery.typeahead.min.js:10
    at String.replace (<anonymous>)
    at a.generateHref (jquery.typeahead.min.js:10)
    at jquery.typeahead.min.js:10
    at a.buildHtmlLayout (jquery.typeahead.min.js:10)
    at a.buildLayout (jquery.typeahead.min.js:10)
    at HTMLInputElement.<anonymous> (jquery.typeahead.min.js:10)
    at HTMLInputElement.dispatch (jquery-3.2.1.min.js:3)
    at HTMLInputElement.q.handle (jquery-3.2.1.min.js:3)
    at Object.trigger (jquery-3.2.1.min.js:4)

[running-coder]

hey @loga4 thanks for reporting! it will be fixed in the next release, rare case when using the |slugify modifier when using the href option, ex: href: "{{url|slugify}}"