Inserting icon inside the input text is not working

[ckarnet]

Issue type

I'm submitting a ... (check one with "x")

• [ ] bug report
• [x] feature request

Issue description

Icon couldn't display inside the input , as per the nebular docs I have done this. No css added. Current behavior:

Icon present outside of the input in the left side

Expected behavior:

Icon should be present inside of the input

Steps to reproduce:

Related code:

insert short code snippets here
```<nb-card size="small">
  <nb-card-body>
    <nb-form-field>
      <nb-icon nbPrefix icon="email-outline" ></nb-icon>
      <input type="text" nbInput  fullWidth />
    </nb-form-field>
  </nb-card-body>
</nb-card>

### Other information:

****

**Angular, Nebular**