Bug in enum type processing

[fbaligand]

Hi,

Given that I have Entity.ts:

export enum Entity {
    firstValue,
    secondValue
}

Then I execute:

typescript-json-schema Entity.ts *

Expected Result:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "Entity": {
            "enum": [
                "firstValue",
                "secondValue"
            ],
            "type": "string"
        }
    }
}

Actual Result:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "Entity": {
            "enum": [
                0,
                1
            ],
            "type": "number"
        }
    }
}