Exclude node_modules folder from tslint

[datencia]

Short description of the problem:

After upgrade to Ionic 3, tslint shows errors even for external typescript libraries inside the node_modules folder.

What behavior are you expecting?

tslint should lint files under src folder only.

Steps to reproduce:

1. create an empty ionic project

   $ ionic start demo-app blank

2. install a dependency which includes the typescript files (e.g. ng2-dynamic-forms/core)

   $ npm install @ng2-dynamic-forms/core

3. import the module into the app module (modify the app.module.ts as follows):

   ...
   import { DynamicFormsCoreModule } from '@ng2-dynamic-forms/core';
   
   @NgModule({
     declarations: [
       MyApp,
       HomePage
     ],
     imports: [
       BrowserModule,
       DynamicFormsCoreModule.forRoot(),
       IonicModule.forRoot(MyApp)
     ],
     ...
   

4. run the linter

   $ npm run lint

Which @ionic/app-scripts version are you using?

2.1.4

Other information: (e.g. stacktraces, related issues, suggestions how to fix, stackoverflow links, forum links, etc)

related issues: #482 & #161