Can't override linterOptions in tslint.json #1463

Short description of the problem:

Adding linterOptions to tslint.json has no effect.

What behavior are you expecting?

Adding linterOptions to tslint.json should work, e.g. exclude some project files from linting.

Steps to reproduce:

1. Create a new project
2. Add some linter options to tslint.json (example below)
3. Edit home page code and introduce a linting error
4. Run ionic-app-scripts lint

{
    "linterOptions": {
        "exclude": ["src/pages/**/*"]
    },
    ...
}

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

3.1.0

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

The above function should be something like this:

const mergedLinterOptions = Object.assign({}, config.linterOptions, linterOptions);
Object.assign(config, { linterOptions: mergedLinterOptions });

Possibly related PR: #1204