Use exception constructor that takes httpCode in asHttpCode method

[gwongz]

No description provided.

[jspaetzel]

Thanks for the contribution @gwongz

How about adding a constructor to HelloSignException for this while we're at it? I'd rather avoid passing null values.

public HelloSignException(String message, Integer httpCode) { this(message, httpCode, null, null); }

Then it can just be throw new HelloSignException("HTTP Code " + code, code); in asHttpCode

[jyoung488]

@jspaetzel looks good to me!

[jspaetzel]

Thanks for the contribution, im going to followup on this in #82