Problem in Angular 6

Hi, According to instructions, I did these steps

`ng new app.. (angular6)`

`npm install angular-signature-pad --save`

```
import { AngularSignaturePadModule } from 'angular-signature-pad';

@NgModule({
imports: [
...
AngularSignaturePadModule.forRoot()
]
...
})
export class AppModule { }
```
`ng serve
`
but i get this error:

> ERROR in src/app/app.module.ts(5,43): error TS2307: Cannot find module 'angular-signature-pad'.

Start by reproducing the reported setup with `ng new`, `npm install angular-signature-pad --save`, and `ng serve`. Inspect the import and module registration in `src/app/app.module.ts` alongside the package's Angular 6 instructions. Done means the module resolves and the application serves without the TS2307 error.

Written by the indexing model from the issue text.