Stepper component doesn't submit form

Issue type

I’m submitting a … (check one with “x”)

• bug report
• feature request

Issue description

Current behavior: I am reproducing the example of stepper with validation showed in the nebular documentation, but, when the “next” button is clicked, the console show the follow warning:

Form submission canceled because the form is not connected

I added the type=“button” attribute and I already don’t get the warning, but the function of submit is not called. The only solution that I found, it is add the “click” event in the button to call to the submit function.

Expected behavior: The form should call to the submit function declared in the “ngSubmit” event of the “form” element when the “next” button is clicked.

Steps to reproduce: Add the stepper component with the following code (Validation example): https://akveo.github.io/nebular/docs/components/stepper/examples#nbsteppercomponent

Other information:

npm, node, OS, Browser

$ node --version
v8.11.3

$ npm --version
6.4.1

Angular, Nebular

 "@angular/cli": "6.0.0",
 "@angular/compiler-cli": "6.0.0",
 "@nebular/bootstrap": "2.0.1",
 "@nebular/theme": "2.0.1",

[IgnacioYanjari]

@Tibing Just go to page, open the dev tools and use the stepper with validations. Press the prev and next buttons and you will notice that the same message appears in the console.

[pedrotcm]

The problem still occurs on the official website itself.