JS files are not linted

[egamma]

Testing: microsoft/vscode#62092

Please see the screenshot below. In the tslint.json there is a jsRule that is validated but there is no diagnostic error

tslint.json

{
    "jsRules": {
        "triple-equals": [
            true,
            "allow-null-check"
        ]
    },
    "defaultSeverity": "warning"
}

test.js

// test a jsRule trippe equals
   let a = 2;

    if (a == 2) {
 
    }