jsdoc incorrectly validates shorthand arrow functions with nested function signatures

jsdoc correctly validates simple short hand arrow functions as such:

``` javascript
/** @param {String} xxx */
var funcName = xxx => xxx + 1;
```

but fails when you add a function signature into the mix

``` javascript
/** @param {String} xxx */
var funcName = xxx => xxx.then(a => a + 1);
```

with the error message `Expected a but got xxx`
