--init should default on strictNullChecks

[tinganho]

I think strictNullChecking should be true by default whenever generating a ts project with --init?

Right now, the options is not generated:

$ tsc --version
Version 2.1.0-dev.20160908

$ tsc --init
message TS6071: Successfully created a tsconfig.json file.

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es5",
        "noImplicitAny": false,
        "sourceMap": false
    }
}

[tinganho]

Oops didn't check #9642