JSDoc extraction doesn't work for index signature object maps

[DanielRosenwasser]

From https://github.com/Azure/azure-documentdb-js-server/blob/a0e6b1b318284838944c7e1b0d1e5848a0788a6b/samples/stored-procedures/bulkDelete.js#L

/**
 * @param x {Object.<string, number>}
 */
function foo(x) {
}

Extracting a JSDoc comment here gives us object<string, number> which

1. Isn't the equivalent type (it's actually equivalent to { [x: string]: number }
2. Is an invalid type reference.